A bit of good news.
I had my 2nd jab March 31st 2021, and later on had an antibody test through my GP which returned Negative (or rather, antibody level was too low to measure).
I had my 3rd jab October 1st.
As luck would have it, I was invited, and duly volunteered, for the NHS Covid Anitbody Test Project the day after. The kit arrived and I took the finger-prick test on October 7th.
Got the result yesterday (October 12th). Positive!
Quote: "Antibodies were found in your blood sample. This means it’s likely you’ve had COVID-19 in the last 6 months, or had the vaccine."
Since I'm more than fairly certain I haven't had Covid, the antibodies must be due to the vaccine, and they must be due to the 3rd jab. There's the good news. Shows that, at least for me and hopefully for others, the 3rd jab is doing its job.
Slight downside is that I don't know the actual level of antibodies - whether only-just, some, a raging torrent. Still, with a booster to come, the outlook is brighter than it was the day before yesterday. I can perhaps reduce my threshold of caution from extremely paranoid to very cautious.
Someone in this forum mentioned how to get on the NHS testing program, I'm sorry I can't find that reference either (my admin must be creaking!). Seems a good idea for as many as poss to get this test (all for free) and report back.