Why not try Chris Knott Insurance a ring on 0800 917 2274 ?
I've been with them for a number of years and was introduced to them through another motoring forum. They are a broker and dont have a wizzy website so the only downside is that you have to talk to someone (heavensforbid!)however when insuring the VTS they were always very good.
covers modifications with cosmetic changes and modded bhp increases of no more than 20bhp and applies to members aged 19 and over for Third Party, Fire & Theft cover and 22 and over for Comprehensive cover. Also people must have at least 1 year NCB and no introductory discounts are allowed, no more than 1 SP/PC/PL conviction offence per driver and minimum premiums are £250 for Comprehensive & £200 for TPFT cover.
They reduced my renewal quote by over £150, reducing my excess to £0 and increased the level of cover inc windscreen stereo contents etc.
Might be worth a call to see what they say.
The only DOWNSIDE is that they dont cover the following postcodes
all M - Manchester, L - Liverpool, OL - Oldham & SK1-12 - Stockport postcodes and Northern Ireland
No connection btw.