@JonnyEnglander I did the reverse journey last weekend in our U.K. registered car, with no problems. My route was France and Luxembourg.
When I checked in at Ashford the U.K. Border Agent asked why I’d been in the U.K. for a week, no evidence of my reason was requested. French control were only interested in my Covid test results. Enroute I saw police cars at two motorway areas I stopped at and neither bothered me, nor did the one I drove past when about 5 miles away from home here.
Good luck if you try it. We’re driving back for the summer in a couple of weeks.