I think E marks are a 'Constuctions and Use' thing, rather than MOT 'inspectable'.

So if you were unlucky enough to be pulled for a VOSA check or a very over enthusiastic plod, they would pick up on non E marked lights, but the MOT would not.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10