One of the defining characteristics of the British people is that they always refer to everything by either its former name, or preferably the name before last. This has been known to irritate VoCSe no end.
It is a well-documented phenomenon that if you change the name of X to Y, the only way you will ever get the British people to start calling it Y is if you then change it again to Z, upon which most people will start calling it Y, a few will keep calling it X, but no-one will call it Z.
Another rule of thumb is that the more misplaced 'funkiness' there is in the new name (e.g. using all-lowercase letters), the more it will be hated and ignored.
For this reason, it's generally a bad idea to try rebranding things in the UK.
The European Union: A large percentage of people still call it the European Community, or the Common Market, or just the Community. (These actually refer to separate entities that were merged into the EU).
BHS, BT, etc.: Back during the Nineties, companies with 'British' in the title decided to go global and just use a meaningless acronym, e.g. British Home Stores became BHS and British Telecom became BT. This totally unmoved the British people, who continued using the former names. BHS has recently given up and gone back to being British Home Stores.
Royal Mail: A contentious one this. The Royal Mail actually changed its name to 'Consignia' briefly a few years ago and started using a logo that looked, appropriately enough, like water draining through a plughole. This caused such an outcry that they changed it back within a few weeks.
Channel 5: Britain got a new terrestrial TV channel back in the Nineties called Channel 5. After a while, and having become associated with softcore porn and wanting to rebrand themselves, they called themselves “five”. Absolutely everyone in the UK still calls it Channel 5.
UK Gold: Similarly, satellite network UK Gold (also UK Drama and other channels) changed its name to 'UKTV Gold', but everyone still uses the old name. It was recently changed again to the face-palmingly stupid 'G.O.L.D.', and that's without telling you what the inane acronym stands for. On the other hand, it did pull off a successful rebranding of UK Gold 2 (via UKTV G2) to “Dave”, an idea which everyone seems to like - it is probably the most referenced satellite TV channel name in mainstream newspapers and TV.