I would run quotes on one (or more) comparison sites. I was concerned over my IS 300h insurance this year, and although my existing provider (Tesco) was asking for 77% more this year than last, I used a comparison site and managed to get renewal for only 15% more with One Click which is with Aegis (I live in Berkshire so not as bad as London but still south-east weighted). Premiums and willingness to insure a particular marque/risk are very insurer dependent.