Imagine if Chaucer wrote the Weights & Measures Regulations and you had to study them at school.
The stuff nightmares are made of.
The e mark and average weight is for everybody and anybody not just UK packers,
It can be used by importers
I would suggest you get a copy of the following
The Weights and Measures (Packaged Goods) Regulations 2006 – Guidance Notes
It is available from the National Weights & Measures Laboratory and it's written in what most of us can recognise as English, well most of it, the statical tests can be challenging.
With regard to evidence that you or your packers are meeting the rules:
13. The Directives also prescribe a specific test procedure (the reference test) which enforcement authorities will use at the premises of packers and importers, when it is necessary to establish whether a particular batch of packages comply with the first two rules. Under the 1986 Regulations and Part V of the Weights and Measures Act, packers and importers were placed under a duty to pass the reference test. The new Regulations instead focus directly on the rules. They place packers under a duty to comply with the three rules. Packers may use whatever quantity control and checking procedures they find convenient, so long as these are sufficiently rigorous to ensure compliance with the three rules. As before, Trading Standards officers may carry out reference tests where they consider this appropriate to check compliance with the first two rules.
This also sets out reasonable well the packers rules and the requirements for the e-mark.