I don't know what copyright law in England allows, specifically for personal backup copies of something you own.

What you could do, is borrow a friend's DVD's and install, using your own CD key. You SHOULD still have the CD key, which is really the biggest thing you need to hang on to. It is unique to you and proof that you bought the game, and allows you to install and play online. You would have to obtain something that lets you play without the DVD though, which is where English law comes into play, and I have no idea what that entails.