They’re back. In a big way, returning from their sell out show at the Edinburgh Festival.

This time they are supporting the Helen and Douglas House hospice for children and young adults with life shortening conditions, to whom they donate all the profits of their shows and CD sales. As if you needed another reason to go.

I have seen Out of the Blue perform before and I can recall each time exactly in a collage of stereophonic swirls, effervescent energy and dodgy dancing. You can’t help but smile when you watch them. Not only are their compositions exceptionally creative and their execution flawless but they also have a unique charm as performers.

A few questionable haircuts and some far from perfect choreography may be the downfall of a lesser troupe. But Out of the Blue can occasionally look like dads at a wedding and still be the envy of every man and the desire of every girl in the audience. (You need only look them up on YouTube to see their American tweenager fan base salivating at the lips and cooing ‘English boys are soooo hot!’).

The fun they have on stage is palpable and more importantly, utterly unpretentious. It feels like you’re watching at a band of fantastically talented friends bouncing around their bedrooms. You soon find yourself grinning back at them, and what’s more, you want to be involved.

Their greatest strength is as an ensemble. It is clear that the individuals who step forward to lead each song are just as equal a part of the symphonic puzzle as the guy beat-boxing at the back.

You can hear the songs coming, giving you for a moment that sense of superiority as you recognise that Beatles riff, and their medleys rise, surge and sink fluidly throughout the sequences. Their set pieces are fun too; look out especially for the gnomish jig during the ‘Dreaming of You’ guitar solo.

The choice of songs is wide (just wait until you here them tackle Coldplay), and they manage most with a unique verve and joy. An encore, you’ll be happy to hear, is pretty much a given.

Perfection is a difficult asperation, especially in something as personal as music; Out of the Blue come pretty close. They ooze charm, and you can’t help but forgive them the slight slip, the (massive and contagious) cheesy smile. It is all, you are constantly asured, really good fun.

In the end that is exactly what Out of the Blue provide, and exactly the reason to go and see them. They aren’t technically the best a cappella group out there, but they are the most irrepressible, and the most fun.

Four stars