The current process for tasking MCA helo's, is the ARCC contact the MRCC responsible for the helo, and then the MRCC scramble that helo. The ARCC's role is to allocate the closet unit.
That is just the way the MCA like it and not the way the rest of the SAR assets in UK are tasked.
Again it makes airborne retasking more difficult especially if you are out of range of FM comms.
In fact i think most current CHC sar flights would prefer not to speak to the ARCC direct.
that is a very professional attitude
Airwave is actually the way forward and SARH flts will need to accept that technology because it is common to ALL the other emergency services and allows you to talk to the POLsA for a search or the paramedic on scene for actual medical updates on the casualty.