Here in UK , like probably elsewhere in the world, FM stations need to be
seperated 200Khz to avoid mutual inteference. A good RX ought with good IF
filtering ought to be able to seperate two 200 Khz spaced FM signals I
think.
But of course stations are only 100Khz apart so it nigh on impossible to
seperate stations under these conditions as far as I know.

Well, if filtering won't sort out the problem, can you seperate the stations
any other way? Can you make a circuit that responds only to the wanted
station when it is just fractionally stronger than the unwanted station?
That's the only thing I can think of, apart from antenna solutions. Do we
have technology these days to do what we thought was impossible in this
case?