Gillian Beasley, chief executive of Peterborough City Council, said: "On Tuesday 21 April we were notified that some voters in three local authority wards of Peterborough; North, Park and Stanground East may have incorrectly received parliamentary election ballot sheets for either North West Cambridgeshire or Peterborough constituencies.
"We immediately contacted the Electoral Commission to discuss with them how best to put this situation right and are now writing to each resident affected explaining what to do next.
“If you live in North, Park or Stanground East wards, have received the wrong parliamentary ballot paper and have not yet returned your ballot paper pack, then you will receive by the end of the week a replacement ballot paper with instructions to complete your local and parliamentary ballot papers correctly.
“If you have already returned your postal vote pack and think you might have received the wrong parliamentary ballot paper, please do not be concerned. We will be able to accept your valid local ballot paper and will be issuing you with a replacement parliamentary ballot paper by the end of the week.
"A mistake was made by the company that printed and posted the ballot forms on our behalf. Our hard working team of election staff is now working round the clock to make sure everybody affected receives new ballot papers and no incorrect votes are counted.
"We are obviously incredibly sorry for the inconvenience caused.
"If anybody has any questions or is worried about their vote they can contact our staff on a dedicated phone hotline 01733 452 282. This website will be updated frequently so please check again for the latest information.”