Thanks to Chris for pointing me in the direction of these.
In terms of transmission dates, I've just listened to the Carthy/Watersons edition and Richard trails the following week's show as featuring Dick Gaughan and Carlene Carter. If GMGough has the right dates in his previous post, that would make the Carthy/Watersons tx date 17 August 1980.
Also worth pointing out that this edition includes two songs by Martin (Sheep Crook and Black Dog & The Hare's Dream) that, to the best of my knowledge, are unavailable anywhere else.