At this time of the year households often receive a questionnaire from local council to complete. The form requires each household to supply details of everyone over the age of 18 living at the address. This is to keep the electoral Register complete and enables the resident to vote at the next election. Failure to add or return this may prevent you from voting at the next election.
Its a fundamental right of a citizen to vote and its a right one should exercise. The Act imposes a penalty of £1000 for failure to return the questionnaire, though unlike in Australia failure to vote is not an offence in the UK.