immigrant marrying in uk,

[Puzzled001]

My neighbour is getting married in April, they have most of the paperwork but have been told that they have to submit a form for a two visa extension after the wedding. I have looked on the Home Office site but cannot find the form (it's the one prior to form M ) My neighbour has spent an inordinate length of time on the phone but keeps getting the run around between departments. Can anyone help with the form number, any guidance appreciated

[Puzzled001]

Above should read ' two year visa extention' after the wedding