With regard to the London ULEZ, if your van is not UK registered you will need to register it with transport for London before entering the Greater London area, you may find that if it is under 3.5 tonne and fairly new you will not have to pay, it is worth registering even if you don't intend to enter the area because the fines are steep if you accidentally enter, for instance if the M25 is closed and you are diverted through part of the zone. With regard to travelling from Toulouse, last year I returned to the UK via St Malo - Portsmouth, this route is handy if you'd like to travel west and around the UK clockwise the M27 which runs along the South coast is close to the port. I mostly use the search for sites app which I've found to be excellent, and as has been said previously it is best to ring pub sites in advance to make sure they have space for you.