DS Developments say that they have checked with Icom and you cannot have the M21 or M27 cos neither have an outlet socket for use with a helmet. Alternative would be the M1EuroV.
a two way fixed intercom system linked to fixed radio say M401 would cost about pounds 1400.00 + VAT
a two way mobile communication ie
2 x 1 earpiece, boom microphone and cable with radio connector to free issue helmet and PTT control fitted to said helmet would cost about pounds 500.00 + VAT
delivery : approx 2 weeks from receipt of order and helmets
I am sure many will find this interesting
web site for DS DEvelopments is www.dsdevelopments.co.uk