It's all here regarding MOT requirements.
MOT checks - direction indicators
To sum up. Indicators must be fitted to any machine with position lamps fitted, with the exception of machines pre-dating 1 Aug 1986 and mopeds. Must flash on/off at between 60&120 per minute. They must be visible from the riding position or a tell-tale light/buzzer fitted in addition.
If not fitted (or only front or only rear fitted) the machine is declared a daytime/clear visibility use only machine.
Interestingly, there is no mention of E-marks as a requirement for an MOT inspection.