The great British marathoning decline

Why have British marathon-running standards declined so dramatically since the Eighties?

This article by David Bradford features Harvey Curtis Sussex Road Race Champion Jon Pepper and Sussex all-time marathon record holder Derek Stevens:
http://bit.ly/1jXquyU

Jon Pepper with Derek Stevens, who ran a 2:12 marathon in 1984

Jon Pepper (right) with Derek Stevens, who ran a 2:12 marathon in 1984