...
- voter number (two letters indicating the polling district, followed by a number)
- voter's name and address
- date of birth (if 18th birthday falls within a year of the register is published)
- if the voter has requested a postal vote
- after an election, an indication of whether or not that voter cast their vote
That an individual individual has a record on the electoral roll is the bedrock on the personal data 'industry' in the UK; it is the platform on which much is built - this is because this record has a) a relatively high degree of assurance that their is an individual at a certain address with this name and date of birth, and b) that this data can be acquired for onward use at relatively small cost (e.g. by credit bureau, marketing services providers etc).