Bit confused by your post, are saying that the UK producers of chocolate are not responsible for the maintaning/ increasing the quality of chocolate and its primarily the EU instead? That seems a very bold claim.
There are numerous companies of varying sizes that produce products of high quality (e.g. Hotel Chocolat, through to small independent craftisans), how exactly are the EU responsible for the drive of this type of chocolate and also 'trying to stop the UK from worsening it's chocolate' for these type of products?
If you are referring specifically to the more mainstream chocolate like cadburys (rather than the above), then I can understand where you are coming from to an extent (e.g. your point of labelling, which can discourage lower cocoa content), though i'd contend your point on how far "the UK' are responsible for the drop in quality. Beyond minimum standards, the overall quality of products are determined by companies and beyond the remit of governments. Also, chocolate under the Cadburys brand, is owned by a large international company and much of its production has shifted offshore, therefore its 'Britishness' has been significantly diluted. Meanwhile its overall quality has dropped due to changes in how the products have been designed and made, which as a sample article alludes to below, has been directed at corporate level
https://www.telegraph.co.uk/food-and-drink/features/the-many-ways-cadbury-is-losing-its-magic/