Below is a copy of part of the testers manual, there is a link to the full manual somwhere on the site. As you will see it depends on the year of your bike but if any are fitted ALL must be fitted AND WORK
Exemptions
If direction indicators are fitted they must meet the
requirements of this inspection, but need not be fitted to a
machine which
cannot exceed 30mph / 50kph, or
was first used before 1 August 1986, or
‘off road’ motor bicycles that are designed to carry only
the rider
‘off road’ motor bicycles with side car designed to carry
the rider and one passenger in the side car.
‘Off road’ motor bicycles are constructed or adapted
primarily for use off road (whether by reason of its tyres,
suspension, ground clearance or otherwise).