The below comes from an article with the actor who plays Mike Tucker. It's long so I've copied and pasted the bit about pay
www.polymathperspective.com/?p=258
Nevertheless, the part has not given Terry the security of a regular income, which an outsider might imagine it to have done. Surprisingly, nobody on The Archers is paid a retainer, so if an actor is not featured for a while, they don’t earn any money.
“At times I’ve thought ‘Oh great, this is wonderful,’ but then suddenly you get a hiccup in bookings and hit what we call the ‘Ambridge black hole’, which is where your character suddenly stops talking and will possibly not utter a word for six to eight months. It is because the script writers are doing other stories and get locked into a cycle of using a particular set of characters. I’m not alone. Some characters haven’t spoken for years!”
“We get paid episode by episode, so if you are in an episode and only have to grunt, you get paid the same as if you had a thousand lines. I believe there are different episode rates for different tiers of actor but I have no idea – nor are we told – what those are.
“It very rarely happens, but one time on The Archers an actor got paid an episode fee just to go ‘Urghhhh’ at the end. That was when Joe Grundy got lost and was discovered collapsed in a field. But they have a budget that allows the casting of a certain number of people per episode, so it would have been accounted for.