It's worse than that:
The Rules of the Air Regulations 1996
"9 Display of lights by aircraft
(2) A flying machine on a United Kingdom aerodrome shall:
(b) ..., display when stationary on the apron by day or night with engines running a red anti-collision light, if fitted."
But:
"(4) Notwithstanding the provisions of this section of these Rules the commander of an aircraft may switch off or reduce the intensity of any flashing light fitted to the aircraft if such a light does or is likely to:
(a) adversely affect the performance of the duties of any member of the flight crew; or
(b) subject an outside observer to unreasonable dazzle."