Thanks to everyone for the quick replied, really helpful.

Make sure you are buying what you think you are buying,
Andy - Thanks for picking up on this, I re-checked the Danfoss product range
and the TP7000 is overkill for my requirements of adding a room stat
to a system which already has a timer. The RT52-RF should do the job and is
much cheaper too. Basically, leave the existing timer to control CH on/off
(day/time/if at all) and add a thermostat to control temperature when the
system is on, much the same as the function of the cylinder stat for the HW.
Clearly Andy's other comments of taking the existing timer out of the system
would be correct if I were to use the TP7000 (a timer and stat) - no point
in having two timers for the CH.

Now to the wiring.

With the info from here plus the Honeywell wiring diagrams (which I found
much clearer than the Danfoss ones) wiring the stat receiver in will
involved
a) Connect the stat receiver electronics live and neutral terminals to the
existing permanent A/C supply terminals used for the valves and existing
timer
b) Logically, "cut" the brown wire currently connected to the CH zone
valve (I say logically as it must already have a break in it to get the
existing timer into the circuit) then
c) Connect the end leading to the motorised valve to the ON terminal in
the stat receiver
d) Connect the end that was leading away from the zone valve the COM
terminal in the stat receiver

Once wired, the stat receiver will have four wires going to it - mains live
and neutral plus two brown wires.

Have I got the wiring correct now?

One other question I forgot to ask regarding wireless control. Given there
are other
wireless devices in the house (network, DECT, Bluetooth) can someone confirm
that adding a wireless stat isn't going to interfere? I couldn't find any
details from Danfoss etc.

Thanks

Jules