Foreign registered, amateur built aircraft are allowed in the UK under the terms of AWN52 (airworthiness notices online at CAA site). This is for a limited period and subject to day/vfr limitations.
Quite a few are imported and run under the PFA auspices. I have been down this route with an RV. If you like, I can send you a copy of my inspection report, which would give you an idea of the depth of the requirement. It seems to typically take about 6 months to jump through all the hoops. Registering in another European country doesn't work really, unless you are mainly based in that country, assuming that you want to stay legal.
The PFA will require verification that it conforms with the plans and any SBs or MPDs that they require. It's best to determine the build standard before you import, as rectification could make it a non-starter.
The types that you mention are all good designs, and if they are well-built and not significantly "customized" shouldn't be too difficult to import. I'd certainly recommend the RVs for all round quality, performance and handling.