You know you've been to an infectiously high-spirited gig when you see grown men (well, large students, anyway) singing multi-part harmonies from Britney Spears songs in the local Sainsburys, round the corner, after the show.

And that really sums up what Out of The Blue is all about - fun, frolicks and really good close-harmony singing.

The first set started with a great video sequence of the group apparently comming from all corners of the globe (and indeed, they'd been there, and taken the videos!), finally converging on the stage door of the New Theatre, and then magically, in person, onto the stage. It was a great opening sequence, and set the stage - quite literally - for what was to follow.

Out of The Blue are a constantly changing group, taking on new members, and saying farewell to veterans every year. That they are able to manage this constant turn-over while remaining a top-quality acapella group is very impressive.

The first set was largely popular songs with one member as soloist, backed by the group. It's amazing to hear the variety of beat-boxing and vocal techniques used to re-imagine songs you'll be used to hearing with a full instrumental band, multi-track studio, and all the tricks of the recording industry, totally re-created for you, live, on stage.

It's equally impressive that these numbers have all been arranged specifically for OOTB by their musical director, Ollie Ralph, and you can hear the skill that has gone into choosing arrangements to suit not only any close-harmony group, but the voices of the group on stage (this year!).

From the inter-song banter and comprehensive program, you get the feeling that this is a very friendly, close-knit group of performers, who really want to get the best out of every opportunity. The first half of the show also gave a lot of solo-time to the newer members of the group, which highlights how inclusive the group is, from the very start.

Part-way through the show there was a quick update and run-down of what the group has been up to so far this (Academic) year. Tales of 'round the world tours' (now we know where the videos came from!) and 'backwards carol singing' gave a quick insight into the whirlwind lifestyle that is being a member of OOTB. A trip to Japan to perform in an international acapella festival, in sold-out 3,500 seater stadiums, and being the only non-professional group there, hints at just how well-known and well-regarded OOTB have become, across the globe.

And rightly so. The second half moved into more 'chorus' territory, with a cleverly-staged 'sing-off/battle of the ballads', some fantastic audience participation (one girl got a birthday present she'll never forget) and some performances by smaller groups with - excellent - niche taste. The rendition of Daft Punk's Harder, Better, Faster, Stronger with accompanying robot-dance moves was really fun, and reminded me of the perfomance by fellow acapella maestros - Fork, of Finland - who sang on the same stage earlier in the year (and indeed, referenced OOTB as their friends in Oxford).

There were some truly stunning soloists. Bayo Randle (the group's oldest member) has a meliflous tenor, Ollie Ralph a soaring falsetto and rich, reverberant bass and Selali Fiamanya an effortless baritone.

The group also runs workshops for local schools in the places they perform, and we were treated to a barn-storming rendition of The Lion Sleeps Tonight, with attendant animal impressions and noises created by about 40 school children! The OOTB boys calmly presided over this happy chaos, seemingly at ease training up the next generation.

Subtle use of pyrotechnics added to the show's joie de vivre. You know a show has made it when they have fireworks! A throughly enjoyable evening was rounded off by a very well-chosen encore and had people, quite literally, dancing into the streets.

I’d like to think that it was my review of the preview (see below) that led to such a turnout at the New Theatre for this latest performance by Oxford’s best loved (shucks, they even have their own GnDs ice cream flavour) all male a cappella group, Out Of The Blue, but I quickly realised that these boys seem to have a loyal fan base created simply out of their own talent.

Tonight, in addition to the music, there were some skits, humorous banter, a video, some must-see incriminating security camera footage during the interval and some pyrotechnics, to boot. As the show was twice as long as the preview, the repertoire was wider, including a brave but excellent ‘mash-up’ of Marvin Gaye and Amy Winehouse, the timeless ‘No Diggity’, some mandatory Coldplay and a curiously contrasting offering of Skinny Love to Fat-Bottomed Girls. Particularly noteworthy was 'Human Drumkit II' (exactly as its name suggests), which showcased the breadth of their talent. Maybe in the future they could foray into different genres or world music?

This time they were also individually miked, which added some serious depth to those glorious harmonies, enhanced the ‘drums’ (incredible as it increasingly appears to be, all the sounds are produced by human voices) but which served as a double-edged sword for the quieter soloists, some of whom were occasionally drowned out by the backing.

The staging looked good, the arrangements were generally taut, and all of it stopped well short of being gimmicky due to both the excellence and good-naturedness of their performance. The camaraderie shown by these young men was palpable, even more so tonight, as several alumni joined the stage to perform the one song that has been maintained since their inception in 2000, ‘The Lion Sleeps Tonight’. And it was just as good – if not better – than when I first heard it over ten years ago.

I had forgotten to mention last time that OOTB have a close relationship with a local children’s hospice, Helen and Douglas House. Their music alone is therapeutic enough but they have also donated around £16,000 to the charity since 2010.

Music can contribute in so many ways to the wellbeing of individuals and of the communities to which they belong. Who needs drugs – medicinal or otherwise – when you can have two hours of OOTB? Since they seem to be accruing accolades faster than Phil Collins can say "gorilla", perhaps we should consider putting them in the British National Formulary: dose - at least four times daily; food - before, with or after; alcohol - definitely not a contraindication. Make sure you get your fix.

When I first arrived in Oxford, a couple of friends persuaded me to go and hear them sing in their newly-formed all male a cappella group, Out Of The Blue (OOTB). So I went along, mainly for a bit of fun and to support my friends. I was blown away. I really recall nothing like it at the time in Oxford, and probably not even in the UK. Twelve years later, after five sell-out Edinburgh Fringe runs, several international performances and a stint on Britain’s Got Talent, the boys – albeit a different cohort – have come back home, to the city where dreams, beneath dreaming spires, really can come true.

Their concept is to deconstruct popular songs (anything from classic pop/rock to jazz, soul and funk) and reconstruct them into a wide repertoire emblazoned with a unique, creative, OOTB stamp. Their methods, which have diversified over the years, involve building harmonies from interwoven melodies and countermelodies, accented with solos, texturing and blending as an artist might work a palette; there also features the ‘mash-up’, where one song is mixed with another. Tonight’s offerings ranged from Marvin Gaye to Amy Winehouse (coincidentally, the wonderful ‘Tears Dry on Their Own’ had accompanied me on the walk to Magdalen College auditorium, with its strange tapestry collection and interesting acoustics).

There were, of course, no instruments, and no conductor to keep time, but that my ears were almost unconscious of this fact – that an orchestra was effectively recreated on stage - is a testament to their talent. The rare occasions where tuning was not entirely pitch perfect were more than compensated for by numerous ‘spine-tingling’ moments of delicious sound that led me to close my eyes and dream of Para-para-paradise (apologies to Coldplay). Usually you look to the back row of a choir to find the bored strategically partnered with the hapless, but this time there was no back row; every person contributed with versatility to the whole, with some outstanding solo performances to enhance - but not outshine - the group.

The choreography (oh yes, they dance, too) flitted between boy band and drunken uncle; whether this is clever marketing I don’t know but, for me, it worked, because it just enhanced their likeability. The only thing I would change is their wardrobe, which made them look just too much like schoolboys.

The great thing about tonight’s press preview was the opportunity to meet the group before and after. It is easy to forget that these young men are students. Of medicine, chemistry, architecture and other subjects, from both Oxford and Brookes; only three actually study music. In addition, many cannot read music and so dual processes of rehearsing with and without written music occur. This fosters interdependence and their camaraderie today was as apparent as their joy at being on stage. Despite the outward polished publicity, which I suppose is an invariable and often necessary consequence of increasing fame, the guys themselves remain refreshingly down-to-earth, not just in their performance, but in their back room chat. Neither geek nor chic, they just are what they are. Which is: just great.

Oxford should be proud of its home grown talent. OOTB’s full performance will be on 11th and 12th June at the New Theatre. Seasoned fans will not be disappointed by the new blood and those who have never experienced it are in for a treat. I have decided that the effect of OOTB is almost subconscious; it catches you unawares and lasts longer than you might expect. I certainly came away from tonight’s fun-filled, toe-tapping preview with a few things I hadn’t expected: a beaming smile across my face, a funky tune in my head and a curious desire to skip all the way home.