Big thanks to CWS, KARFA and orbitmic for your thoughts over the last page or so. I do hope I bump into you at a future "do" and will gladly buy you all a pint for the wonderful assistance and advice you give posters on here.
I am by no means a lawyer either but I'm glad to see we have reached consensus on the SI amendment requiring those quarantining from exempt countries prior to 10 July to continue to do so until their 14 days are up, however frustrating and illogical that may be. And that exiting to a suitable location and returning again from Friday won't raise any red flags.
Now I have the fun task of deciding where to go, and indeed whether to go. I'm WFH indefinitely and can easily get supermarket deliveries, I'd just quite like to go to the pub with friends this weekend!