You can hear it by going to Midweek's website page and pressing LISTEN AGAIN. McTell starts his bit at about 22mins50 in, though he does pitch in earlier as well.
He talks about this and that, for instance how he got the line "It's a long way from Clare to here" off a fellow builder, from Ireland, while he was working on a building site and chatting to him about coming to the UK. If the chap had said "It's a long way from here to Clare", says McTell, it's likely no song would have been sparked off (being more a straightforward statement of geographical fact). Also, he says he quite likes that it has sometimes been credited as Trad.