My friends wrote their own and agreed them with the registrar...
The actual minimum vows for it to be legal are quoted on the website below, reproduced here:
The Statutory Words
The minimum vows required for your marriage to be legal are as follows. These words must be said by both of you and be used somewhere in your ceremony. You will usually be allowed to add your own choice of vows before or after the statutory words:
In England and Wales the statutory declaration is:
"I do solemnly declare that I know not of any lawful impediment why I, [your name], may not be joined in matrimony to [your partner's name]."
followed by these contracting words:
"I call upon these persons here present to witness that I, [your name], do take thee [your partner's name] to be my lawful wedded husband [or wife]."
In Scotland the couple say:
"I solemnly declare that I know of no legal impediment why I, [your name], may not be joined in matrimony to [your partner's name]. I accept [and [or wife]."
In Northern Ireland the statutory declaration is:
"I know of no lawful impediment why I, [your name], may not be joined in matrimony to [your partner's name]. I, [your name], take you [your partner's name] to be my lawful wedded husband [or wife]."