I have a spare relay I'm sure in one of my scrap cars you can test it on, rare problem never heard of anyone having that issue. Just check all your ground wiring and earth connections to the indicator looms and just double check all bulbs don't forget the ones in the wings as well. I'm sure it's something simple, did you notice this before the MOT? or did it start doing this at the MOT? not MOT centre trying to rip you off?