RAF SAR helicopters are not really getting new radios!!
The new ICOM radio is a hand held, marine band, transceiver that the Winchman will carry. New rules on MRT frequencies required a new radio as the one that was previously carried (in addition to the polycon) did not have the new frequencies. The polycon operates as a 'remote' intercom and can only communicate with the base station on the helicopter (or another polycon fitted helicopter). The ICOM unit can talk to anyone using normal marine frequencies. This includes the Coastguard and civilian and military MRT's.
The polycon system was supposed to be fitted with a marine band 'card' to enable it to do this but there are problems with it at the moment (i'm not exactly sure what).
EDIT: It does not cost very much (about 1/10th of the new MRT radio).