Highway Code here :-
http://www.highwaycode.gov.uk/19.htm0
Code 177 states When using a driveway, reverse in and drive out if you can. I think that if you are able to reverse out of a driveway into a road then you are able to reverse from a road into the driveway.
trevHCS - It doesn't matter if reversing up a driveway into a std. garage isn't easy, if someone finds it difficult then should learn how reverse properly. Anyway, it's far safer to do that than to reverse onto a road.
derekpara - even if you have to do the reversing in a congested area like London then whichever way you do the reversing you are going to impede drivers at some stage; far safer to hold them up while you reverse in as you have no idea when you will have to leave your driveway, it could be at a peak hour if there is an emergency so it is safer to do that forwards than backwards.
It doesn't matter if it illegal or not, it is just far safer for everyone to reverse into a driveway and drive out.