The email from the council said:
Their website has some more worrying information:Please bring the documents listed below with you on the day. Failure to bring these documents may result in you not being able to receive your naturalisation certificate on the day.
1) A copy of the ‘Home Office Invitation’ letter or email (either printed or digital).
This letter is sent to you from the Home Office and not Hackney Registration Services. If for any reason you have not received your Home Office invitation letter in time for your ceremony, please bring two forms of photographic ID with you on the day instead.
Should I be worried?Each new citizen will receive two emails or letters from the Home Office. The first will be informing you of the decision of your application. The second will advise you that you can arrange your ceremony with us. If you haven’t received both, it means we don’t have your naturalisation certificate and can’t offer you a ceremony until we get it.