Tallsar - I think the diversion issue is still relevant and the reason it doesn't happen often is exactly because of where the bases are located.
If you have to divert after a messy rescue (lots of blood and guts in the back) unless you can get home you have no way of sanitizing the aircraft nor re-stocking the medical kit so you are left in the wrong place in what is effectively a U/S aircraft.
Appropriate recovery aids are expensive (we have just had our ILS replaced so we know!) which means inland bases would have to be sited on an airport with an ILS (still with a 150' DH) where a coastal base would allow an internal radar letdown to the beach and a hover taxi back to dispersal in far worse conditions.
Trying to move away from coastal bases ignores the fact that we are an island nation with a lot of coastline and both tourism and maritime trade and fishing generate the majority of our jobs. Add in the Lake District and Snowdonia being easily accessible from the sea and there seems little reason to have a SAR base anywhere except the coast.
The concept of inland bases was, I think, where the Fire and Rescue Service were going when they mooted the idea of having their own helicopters and it doesn't seem to have got very far.