We use A to Z London books that have proved invaluable as DH has to come to London for conferences/ courses and I tag along and am let loose in London! We have a large one for planning and a small one for my backpack. Available from good book shops, not just in London. I salute you for doing this trip. I haven't driven in the centre of London, but haven't needed to. My driving challenge is driving in the USA, which I have avoided up to now. I am lassoing my son, not my DH, for educating me in the differences, apart from driving on the wrong side of the road!