Thanks to cee - b
I have checked-out
http://www.motuk.com/bike/manual.asp and discovered the following, which I find a little confusing in parts or is my advancing which is the problem?
Machines first used before 1 April 1986
must have a stop lamp that operates from at least one brake control.
Machines first used on or after 1 April 1986
must have a stop lamp that operates from both brake controls.
Stop lamp: All machines, except those which have neither front nor rear position lamps, or has such lamps permanently disconnected, painted over or masked that are only used during daylight hours, and not used at times of seriously reduced visibility
Horn (Audible Warning) A motor bicycle first used before
1 August 1973 may be fitted with a bulb horn.