Moderator, feel free to move, I couldn't find the right thread

I land in UK from USA on Thursday
I'm fully Vaccinated
So as I understand it, I need a pre USA departure COVID test and then on arrival in UK a day 2 PCR arrival test.
I return on Monday (4 days later)

Can I use my PCR day 2 test as my Pre departure UK test. I'm thinking I do day 2 test on Friday and that is 3 days before departure?