UK Biobank survey.

This is checking whether people have Covid 19 antibodies. Just a pinprick , then you test it yourself. Very easy to do.
It turns out that though I have had one vaccination, I do not have antibodies. Not too happy about that.

A bit more info on this from the Imperial website.

We receive many emails from people who have received one of the authorised vaccines in the UK, but then take an antibody test that shows they do not have antibodies against the virus.
They are worried this means the vaccine has not worked – but this is not necessarily the case. Although an antibody test may be able to tell if you have been previously infected with SARS-CoV-2, it will not be able to tell if you are protected following a vaccine.
Many antibody tests detect a type of protein in the SARS-CoV-2 virus called the N-protein. This protein is not found in most COVID-19 vaccines. So even after having a COVID-19 vaccine, in most cases there will not be an antibody response against the N protein, and an antibody test will be negative.