If you want to get an idea of how many second doses should be coming up, just look on the vaccination graphs for the number of first given 10-12 weeks ago.
So 20th Jan there were close to 5million cumulative first does given. 31st Jan was just over 9 million.
We are currently at 2.3 million second jabs. (~everyone who had first jabs to 11th Jan).
(Personal good news is that number now includes both my parents.)