I use SH.uk
It’s nice and simple, and you can create a shareable link of your results (note that when using that link your name is included)
There is a wide range of NHS and private testing available in person or by post, and there will be a few threads on here with people’s experiences on them
It may depend on how timely you want results, on a routine basis SH works for me. I usually have results the next day once they have received the samples, failing that it’s been the second day.
I can order a pack and get results in the same week