Wayfarersonbaby thanks for your two posts! they cleared up something that was puzzling me about voter information.
About 5 minutes after I got back from voting yesterday the doorbell rang and it was a canvasser. They asked for DH by name. I said he was busy, what did they want? (I was talking to her over an intercom, we live in a flat).
She said she was canvassing on behalf of X Party and had DH voted yet? I thought that was an odd question, and possibly slightly sexist as she didn't ask if I had voted. I just said that we had both voted and put the intercom down, but it left me slightly troubled.
I started to ponder if they had access to the lists showing those who had voted that day and who hadn't - but they would have been remarkably quick off the mark as I had voted less than 10 minutes previously (polling station 3 minutes walk from my flat).
I didn't realise that the electoral shows the fact that you have voted in previous elections or not 
DH is not a British national, although has Indefinite Leave to Remain status so has the right to vote here. However, and much to my annoyance and slight shame, he has only ever voted once and that was in the EU Referendum. I, however, vote every time.
So I guess she probably didn't want to bother talking to me as it was already gone 9pm and she guessed that I had probably already cast my vote! I think she was hoping to get DH up off his butt and down to the polling station to vote for her candidate.
All this stuff around voter profiling is going to be much harder in future elections. Data protection law changes next year with the advent of the General Data Protection Regulation. No one will be able to profile/ wealth screen/ whatever screen without explicit written consent.