I'm not a lawyer and this isn't legal advice.
If you are arguing that a contract hasn't been fulfilled then it is the bare recorded contract that will be looked at, not the fairness of the whole situation. If your contract doesn't require delivery by a certain date, then delivery could be at any reasonable date. We know that in the past people have had to wait up to 9 months for delivery due to supply and demand. That was just tough. We also know that when there were delays and we were coming up to the big VED changes in 2017, some people had dealers who guaranteed delivery before April 1, or they would pick up the VED increase. Those guys effectively had a delivery date written into their contract and a remedy if the delivery date was passed.
Edit: forgot to say - if you booked a holiday without a delivery date in your contract, you probably won't get much from the courts. If you booked a holiday given that the dealer told you the van was about to arrive, then the dealer may feel that they should make a goodwill gesture.
In the end you do what you need to do, but legal action is expensive and very stressful. For the sake of an easy life I would see what I could get from the dealer (things that they can easily supply) and move on.