Just pretend that the previous 2 or 3 times you bought a Martin or Eliza Carthy album, or went to a gig, it cost £1 more. Think of it that way. Like a tip.
To all those pointing out that there are more deserving cases: I'm sure Martin and Eliza would be equally glad to hear that their plight has prompted you to give £5 to Medecins San Frontieres, or a Palestinian refugee charity or whatever; because they are nice people who I'm sure know only too well that there are plenty worse off than them.