Any suggestions as to how I can clear the spreading St Johns Wort from my long border

well it will have to be something like SBK brush/scrub killer. My daughter has the same problem and she is very reluctant to use chemicals as she is a wildlife conservationist. But sometimes that is the only option if 'dig it out' is not feasible.

As you have other plants in the border you need to treat the St. John's Wort while not affecting the rest. You can use a weedkiller mixed with a wallpaper paste and paint the weeds or cut the bottom of an empty soft drinks container and cover the weed and spray into the container. I would look to do this on a sunny, rain-free day so it's not washed off. Might take a while but should do the trick.

Thankyou Seaburn and Jimmy.....