they were not eligible to do so, F2. . .

though they were so eligible, either of them did not F3. . . consent to its formation F4, or.

at the time of registration one of them who was capable of consenting to the formation of the civil partnership purported to give consent but did so by reason only of duress or error.

error as to the nature of civil partnership, or

a mistaken belief held by a person (“A”) that the other person with whom A purported to register a civil partnership was the person with whom A had agreed to register a civil partnership.