Why is there 2 or 3 people outside who take the number off the card, then when you go inside to vote they take it again just before giving you a ballot paper?
You actually don't NEED to take your card! It's just for ease of crossing you off the register. The people outside are usually candidates' helpers, who MAY whizz around knocking doors and offering lifts to people who haven't been to vote.
Telling is relatively rare now as to get the best from it you need a detailed knowedge of every ward in a constituency to make it work effectively and there arent that many volunteers or people with the necessary skills anymore.
horseshoes you are absolutely correct, when I was a young member of a political party, I used to do that on election night, very few takers of a free lift to Polling station.
These "tellers" are not necessarily as harmless as they would like you to believe. Like all aspects of the political process they have been corrupted by the zealots and those who like to operate using black/brownshirt tactics.