At first, you think that Gareth Gates is having a little joke...
... but the mention of the second song really does suggest that Gareth was actually being straight faced.
He presumably realises that, set against McCartney's annual earnings, the royalties from a Gareth Gates song would probably barely make a tinkle in a pewter mug, doesn't he? And, also, since he was paying McCartney for the rights to a song that McCartney owned, in what way would that put McCartney into Gates' debt? Does Gates think that when he buys a pasty from Greggs, somehow this means he has a moral right to go to the bakers' Christmas staff do?
Gareth, Gareth... it might take a little more than merely copying someone else's song for that to happen, you understand.