M4 Berkshire Vans with "EN" - Camera Vans?

[anonymous-user]

Was going along the M4 from Newbury (J13) to Maidenhead (J8/9) on Thursday afternoon. On one of the bridges there were about 3 open back trucks (which looked like roadworks vehicles) and one transit sized van which was totally white apart from the letters EN on the side. The rear side panel of this van was of black glass/plastic (did not look like it could be opened) and wondered if this was some sort fo stealth camera van. I was under the impression that camera vans needed some sort of marking, but maybe not?