Hi Jessie, four years later... did you manage to find out the band for this song?? I came across your question as I was this morning trying to find out the name of the band. Like you, I remember it from the early 1980s but cannot work out who it was recorded by. I actually recorded it off the radio on 24th December 1981 onto a cassette I still have! It was played that morning on BBC Radio 2 by Terry Wogan as I left the cassette recorder running and can hear him speaking over the fade-out of the record! Your memory is accurate (it was "Ol' M4" not "old ten four" as reference to the trusty motorway from London to the wild west!). I didn't record the whole song, but from partway through. I've managed to get these lyrics from listening to it just now:
"I settled up my subscription, paid up my membership; I've got a bullet belt and a forty-five on low down on my hip; well the stetson hat don't fit too well, and the boots still tend to rub; but it's worth being number 76 in my local Lone Star club... I'm a Friday night cowboy, with a long hard ride in store; I've saddled up my Cortina, and I'm coming in on the ol' M4; I'm a Friday night cowboy, in a weekend wonderland, deep inside what I really wanna be, is another hired hand."
I remember it as being a novelty record, the type that Terry would play, with very English lyrics, sung in a cockney 'lads' style, fast and with country music backing, and it was well produced. Unfortunately I cannot (yet) find the name of the band!