I had the same with Admiral - big raise in the price at the end of year 1 for our multi-car. I was told a load of old clap-trap.
Raise in Insurance Premium Tax
General raise in premiums
I went to Churchill who proved to be terrible and I will be leaving them at the end of the year.
One thing to watch with all the big providers now is the addition of hidden charges that are being added all over the place to raise money.
Change car sir ? £50
Change job sir ? £50 and possible changes
Change registration plate on car sir ? £50
Sell car sir ? £50