They are just doing a straw poll to gauge how many in the area do vote, used to earn pocket money doing it myself. If you don`t want to tell them just say No.
they may be 'party' workers- keeping a record on the number of voters and who has voted
you do not need to give them your number
party workers are usually in the main voting hall tho' and 'tick off' your number when the polling staff call it out
They always ask me and I don't tell them. Up to today I have only had 1 party deliver any bumpf through my letter box. Today all the main parties have deposited their papers on me. I wouldn't mind but the recycling bin was emptied early this morning. I like to leave it quite late to vote and then we shall see if they come round to offer me a lift to the poll!
beejay is right,
At our Polling Station (the village hall) the party workers take it in turns to sit and ask you your name and number(you are under NO obligation to give it however).
This is so they can try and get anyone who hasn't voted into the Polling Station before it closes.
In our village (thank god) they are very civilsed and co~operate with each other.
Some party workers will go and collect inform or elderly voters in their own car to enable them to vote.