Lol... Brits are traditionally bad at complaining! In France or Italy it's normal, as we expect high standards. Next time, think of it not necessarily as a complaint, but as constructive cirticism, thus allowing the restaurant an opportunity to do better next time.
If you do it in the right way, and be polite but firm, then you'll usually always achieve a positive result. Most good establishments want to know what their customers think of the food and service they've received and whether or not they can improve:)
Marco.