I agree with the OP - it's a frustrating issue, especially it seems with Italian restaurants in London. I remember one where I had to ask five times and it took over an hour from asking for the bill to getting out of the door.

Having said that, it's better than at so many US restaurants where they hand you the bill while you are still eating, desperate to shoo you out of the restaurant. That really irritates me and deserves a far bigger reduction in the tip.