Thanks to this forum !
We are just back from 11 days in London.
The tips and advice gleaned from this forum before we left were invaluable and helped make our trip a breeze (well there certainly was a breeze and I wasn't going to mention the weather - 3 degrees celcius when we left London, 34 degrees celcius when we got home).
Despite the 23 hour journey each way we are pencilled in to do it again next winter.
Thanks everyone for your time and knowledge - a great help.