We are an island nation and trade and migrate accordingly over the oceans.
To that end in the future we will simply purchase an aircraft that is or has the following:
Reliable and reasonably modern and commercially viable, like what good airlines buy.
Long or very long range from a UK runway.
Has radar and other modern aids to locate people unfortunate enough to be in and at the mercy of the seas.
Be able to communicate and therefore steer other rescuers to the scene.
Possibly drop aid to people in the water.
And fly back to the UK again without crashing, or running out of fuel and crashing.
Seriously, that's about it.
So what is really needed is just a long range/long endurance SAR platform? Really? That could be done very cheaply with a decent radar installed in any number of biz jets or even a biz turbo prop. If a multi-role capability is desired so the airplane could be used for something else between SAR missions, then the C-27J would make a good and relatively cheap platform. USCG is doing exactly that.