I faced this issue late November on the 350z and last month on a 16 year old prelude. When it came to the 350z having insured it no problem in my first year i struggled on second year massively. Despite having 5 years on a completely clean licence, 5 years NCB and being the right side of 25, I couldn't get much less then £750 depsite paying £600 in my first year on the Z. The woman at prestige, Tim is a poster here said that 28 is the new 25.
Last month my renewal came up on the daily Honda prelude. A simple 16 year old car valued at £500 with a painfully slow 2.0 L engine. My renewal quote was £425 with a £45 pound admin fee (which I refused to pay on the basis of being a continuing customer) I went looking on comparison websites and to my horror the cheapest I could get was £1000. Even ringing around proved useless. Insurance seems to have royally lost its marbles