This reads like a tyre problem. It could be a serious alignment issue or it could be that the van simply has the wrong wheels and tyres fitted. It isn't uncommon for some people to get confused and fit car alloys and tyres to a van, which results in problems when it comes to handling and tyre wear. First things first, take it back to the dealer. Ask them to fix the problem or refund your money. Remember, the dealer is liable for any faults that develop within the first six months from the date of sale, so don't let them fob you off with any excuses. Personally, I’d ask them to replace the tyres to ensure they all have matching load and speed ratings. For your consumer rights, see: www.honestjohn.co.uk/faq/consumer-rights/