Corsa-B.uk - Vauxhall, Opel and Holden Corsa B Owners Club

when i bought my car a few weeks ago i realised it had an after market alarm, i've some lookin on the internet an found out it is actually a thatcham cateogry 1, but i also found some information that stays i need to have some sort of certificate before i can declare it on my insurence, but of course i dont have the certificate, SO.... if i tell the insurence company its a standard alarm will my insurence be void or should i remove the alarm? or do i actually need a certificate?

help.

any and all help welcome.