@Glos Guy if unt up’s the VAT rate, I reckon it will increase at 12am on January 1st next year.
I was VAT registered from early 1990’s to 2015. If the VAT rate increased during a job, the customer if they asked to pay for the work already carried out at the current VAT rate I would allow it and in many respects invoice for more if they were willing so they were charged less at a higher rate of VAT on completion of the work. A customer would often provide a nice tip at the end as cash in hand.
It was not in my interest to do this as I could claim more VAT back at the increased rate, if they were billed on comletion. Most of my work was was to local authoritis/NHS and emergency services so it didn’t matter as they could also claim VAT back. Private customers were the ones affected so would be willing to bill x amount early.
Now take a greedy car dealership. It would be in their best interests to charge at the higher VAT rate as they could claim more back, as shown in my reply to @myself33.
There is no harm asking the dealership to play with their figures and issue/amend your invoice once warning has been given on what/if the new VAT rate will be, so you end up paying no more then when you signed on the dotted line. At the very least they could meet you half way and split the difference, but these are dealerships we were talking about.