@MrsHuntGeneNotJeremyObviously
My parents had Pfizer, so I think there must be second doses kept back.
Pfizer is still coming in, at present, and there will be a supply (a few days? WHo knows? The UK government has been very cagey) in the country.
There won't be all the second doses in a warehouse somewhere as that would defeat the purpose of increasing the time between doses to speed the primary dose roll out.
I'm glad your patents have had yours without issue.