I wish to bring a remote CH motorized valve (Honeywell make) into
use. It wasn't connected when the CH was installed as the valve was
a last minute thought and no suitable cable was to hand. Up to now (8
years!) it has been left in the ON position.

Depending on route chosen, it will require 5 to 8m of cable to connect
to the main CH controller. The cable into the valve is 5 way x 0.8mm
sq (ie 1.0mm dia) - 4 control lines plus earth. The valve operates at
240V, so the cable needs to be rated for mains.

For preference I should like to use standard elec backing boxes to
house the connections at each end, and bury the cable run under the
wall plaster.

Please can anyone suggest a suitable cable & source?

TIA