The last couple of times I've seen his programme, he's sung 'Love Me For A Reason', which was a hit for the Osmonds, and then for Boyzone. However, I think the fact that his guests were Donny Osmond one week and Louis Walsh the next might have had something to do with that, so I'm not sure if this is the song you're after!
He loves anything by Queen and sings "Don't stop me now" in the titles. Can't think of any other song he sings all the time.
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And yes, I think he's brilliant too. What a concept, to have an hour long show in order of the Great British way of life. Shows you we can laugh at ourselves as well as at others