Try www.confused.com and www.insuresupermarket.com before you do anything else. For me, as my car is 'modified' (cone air filter ), only Admiral would quote (same quote from both), but they were £100 cheaper than Elephant wanted to renew, taking me down to about £240 this year. Ah the joys of getting old.
Also, don't pay your insurance in instalments (if that's what you meant by £200 upfront), you're basically taking out a personal loan to pay the insurance and they don't give you a competitive rate- usually 15-20% which is a lot. If you can, find a credit card that gives you 0% for 6 or 9 months on purchases and use that to pay upfront (although obviously you must then be disciplined about paying it off, set up a direct debit ideally). If not, you should still be able to get a personal loan from a bank or whatever at a much lower rate than 15%- less than 10% should be easy to find.
www.moneysavingexpert.com is the place to look for the best credit card and loan deals.