I thought I would just let you know about NOVA in the UK - introduced April 2013.
Two years ago we moved to France and as a good law abiding resident I managed to get our Landrover Discovery and (UK only make) trailer immatriculated and even tried, unsuccessfully as the manufacturer no longer existed, to get a moped done too.
Because the goal posts moved in France we have returned to the UK to sell our UK property and want to re-register in UK. Now NOVA (Notification Of Vehcle Arrivals) exists: Basically all vehicles with an engine have to be notified to HMRC before you can even begin to re-register a vehicle with DVLA in the UK. Despite originally buying the vehicles in the UK we still have to go through this process, shouldn't be difficult but it is a hassle - but I originally read I only had 14 days but I think in these circumstances you just inform them when you decide to re-register, within 6 months, the sooner the better - for them obviously.