Just a quick update to post the text of my trans marriage restoration amendment which I am now informed has been tabled by my MP, Julian Huppert (many thanks):

Page 10, line 3 (Section 9), after end insert:
(8) Where a civil partnership formed under part 1, section 96 of the Civil Partnership Act (Civil Partnership with former spouse) is converted into a marriage under this section —

(a) the civil partnership ends on the conversion, and
(b) if both partners so elect,
(c) the resulting marriage is to be treated as having subsisted since the marriage dissolved under schedule 2 of the Gender Recognition Act 2004 was formed.

If we get mixed sex civil partnership, an equivalent amendment will be needed to restore those as well, but we’ll cross that bridge if we come to it.