Ah that wouldn't have been an issue for me. I originally took my policy out on a stock MX5 then fitted the turbo kit drove it a few months @ 200bhp then increased it in stages
They're an odd company, I've always found them really quite rude on the phone and usually uncompetitive if I can even get a quote. Having said that I used to find Chris Knott constantly expensive then one year the price worked for me and they were a brilliant company to deal with once on policy. Possibly the only insurer i havent haggled with at renewal time as they were just so much cheaper than anyone else. I imagine most of the specialist insurers are good to deal with once they actually have you insured as it's partly how they will keep business.