How do I find a Traffic Regulation Order for a motorway? Options

[Abonae]

I've recently received a NIP for speeding on the M5 J16-17, where there is a variable speed limit system. The offence stated is: Exceeding a variable speed limit - automatic camera device. The NIP states that this was:

Contrary to the above Local Traffic Order and section 17(2), (3) and (4) of the Road Traffic Regulation Act 1984 and Schedule 2 to the Road Traffic Offenders Act 1988.

There are no details of the Local Traffic Order that I can find on the form.

My questions are:

1. how significant a defect is the absence of a definition or even the name of a Local Traffic Order, and,
2. Where can I find a copy of the relevant order?

Thanks in advance

Abo