I think Peter Bellamy filled in the missing two lines with:

So when the sailor pulled on the ol' string,
She's rolled back the blankets and pulled Jack in.

It's on 'Won't You Go My Way' on ARGO ZFB 37
He sang a lot of Sam Larner and Harry Cox songs at that time. It could be from either of them.

Martin Carthy use to sing a song with a similar theme called 'Do Me Ama'. A different version of the same song did the rounds at The Old Crown club at Birmingham in the mid 1970s which I still occasionally do.