Re: Lack of a secret ballot is a greater problem
The polling number is on the back of the ballot paper. When the papers are being counted, they are kept face-up so the candidates and their agents lurking behind those doing the counting do not see the polling number. Traditionally the only time the polling number is reconnected to the voter ID is when there are court actions over the vote.
Postal votes are slightly different. As they are received in the days before the election, they are vetted by election staff and then put into a ballot box ready for counting. As a candidate myself, I have wondered what checks there are on that vetting. The candidates are not invited to oversee things for obvious reasons. Does the Electoral Commission do any overseeing here?