Paul McCartney -- Hunting for Free Nets T-Shirt in London

Paul McCartney is REFUSING to give up his quest to score a free Nets t-shirt ... 'cause the Beatle followed the team to London for a second chance at grabbing a free souvenir.

The Nets took on the Hawks at 02 Arena in London today ... where McCartney joined up with his daughter's family -- presumably to increase his odds of nabbing a fan giveaway.

In case you missed it ... Paul was visibly devastated at a Nets game in Brooklyn last month, when he failed to catch one of those t-shirts the cheerleaders toss into the crowd during timeouts.

No word on whether Paul caught anything tonight ... but the good news is he can always afford to keep trying.

As for Nets star Joe Johnson, he showed no signs of a hangover after dropping $10K at a London nightclub Monday night -- putting up 29 points on the Hawks in a 127-110 Nets win.