Liverpool Victoria dont like modifications any more. Neither do Norwich Union. Most companies accept simple mods like alloys, side skirts or cosmetic mods, but as soon as you start modifying your car to improve performance, top speed or acceleration then they wont touch you. In your case, the suspension will push the premium up.
http://www.admiral.comwww.admiral.com - they were good for me this year with my dad as a named driver. They wanted 1400 just for me, ended up with a quote of just under 900 (22 with 5yrs NCB, clio 1.4 16v with alloys, suspension, brakes, filter, zorst, external decorative mods, policy also included protected ncb and b/d cover).
also try endsleigh insurance (if your a student, you get 10% discount). was with them last year and theyre ok for some mods.
avoid tescos like the plague. they do cheap quotes but lots of people have had problems with them with regards to claimin gor using their services such as legal cover.