With regards to tv/sat/fm, planning to put a 'loftbox' in the understairs
cupboard with a couple of CT100 cables running to the lounge and a single
CT100 cable runing o each bedroom. In the lounge I would have a tv/sat/fm
triplexer with additional tv and tel connections (MK part K3563 WHI) and
the
bedooms I would have tv/fm diplexers. Would this meet my requirement to
have
tv/sat/fm in each room? (I do understand that with this setup I would be
restricted to viewing the same sat channel in each room)

If you want to control the sat box with "magic eye" remote extenders in each
room, make sure the triplexer can deal with the DC control voltage.

An alternative, but with no BT socket is to get a Clipsal 1 gang 4 way
modular socket (Clipsal E34WE), an "F" coax output and 3 "UHF TV/FM"
modules.
Connect satellite feed to the "F" connector, TV and FM aerial leads to "UHF
modules", and then a return UHF from the sat box aerial output 2 (and
video/DVD etc) up the third "UHF module" back into the loft.
Now get a cheap aerial splitter instead of a loftbox, and distribute the
sat/tv signal to all rooms. If you want FM, either diplex the signals into
the UHF or run extra coax to each bedroom socket.

Unfortunately Clipsal don't make a BT phone socket, though they do make a
Cat 5 socket.
This setup means a bit more coax laying, but the splitter should be cheaper
than the loftbox (8way £30vs.£90, 4way £25vs.£70), the socket is 1 gang, and
the satellite signal is tampered with a lot less (which can be important
with a small dish / weak signal).