Lets do the easy first.
Ban anything with the CE mark this is built / made in
Probably a host of others.
Country of Origin Cannot even get as close as Continent of Origin
What we need is a 'Made in Britain' mark for goods and services that are predominately grown or made in Britain. So, for example, lettuce grown in the UK qualifies for the mark; lettuce flow in from abroad does not. A car with 60% of it's components actually made in the UK qualifies; a car with less than 60% does not. A further criteria could be that the company concerned must have its European HQ in the UK and pay the bulk of its tax here.
That way we don't really have to police CE marks or or 'country of origin' we just need to police the 'Made in Britain' mark. If that becomes regarded as utterly reliable, people can come to their own judgements on how reliable other certification systems are.
I'd probably be happy to pay a few quid more for a product if I knew the money was going back into the UK economy and not to some overseas provider of short lived crap. And longer term, the governments tax take would go up - so more money for public services without raising the tax rate.