I am offering an advice how to get 2 independent licenses and credit flight hours. I haven't found any way to convert a FAA CPL to the EASA one just with a check ride. Probably you're talking about a validation? In that case the license will be valid for 1 year only, and you will have to keep your currency for both. I don't know how it works in UK, but for full unrestricted lifetime EASA license I don't know any other way than studying and passing theoretical subjects and undergoing required minimum amount of training. At least according to EASA FCL.
Even for a validation, it cannot be done so easily (at least according to the EASA regulations:
https://www.easa.europa.eu/faq/19185).
If you know how to do it more easily, please describe it, a lot of FAA-certified pilots willing to obtain an EASA license will highly appreciate it since they are currently undergoing the process I described above. And so did I.