thanks for the replys, i may have found a solution.
my dad is a retired refrigeration engineer and i picked his brains about it. he said theres a fur like bacteria that grows in the air-con system, sounds quite nasty but no harm in the air-con just releases a smell when initally turned on. his suggestion was exacully what robbierolex said, you spray it in the vents? and it kills the germs.
when i get chance im going to pop down to halfords and give it a try. also it is book in this monday for a service, pollen filter will be chainge then for an added bonus.
ill let you know how i get on.