Thank you, PECS, but it's not Nancy Sinatra. I've been doing some searches and have discovered it's a very common term in song lyrics but not the actual song yet. I've got MrBags on the search too. I think it must be from the 60s or 70s as I haven't heard much pop music since then–not my thing.
I hummed the tune to MrB and he recognised it so it's not just my memory playing tricks .
To think that London, or anywhere else for that matter, does not belong to any one demographic