The singer, a tinker, meets Sally Anne and takes her into his Bedford Van. She proposes, they marry, and honeymoon in Glasgow. He is stopped for driving drunk. Sally "took sick" from overeating. When "a big dame" makes a pass at him Sally clouts her.
The singer, in the song, is from Springtown, a post World War 2 slum outside Derry City, closed in 1967 and demolished (source: McBride). When stopped in Dublin he is given a breathalyser test. The song ends with a warning not to be too quick to pick up a girl in your Bedford Van: you're likely to end by being married. - BS