Not much you can do if mixed with other plants apart form hand digging. If there are any stray 'buttercups' that aren't near plants, then you could spray these and this will eventually work its way into the root system, but will take a long time. Perseverance i think is best.
If there are any buttercups near the base of plants, you can mix up some weedkiller in a hand spray and place a yoghurt pot with bottom cut off over the weed so only the weed leaves are enclosed, and then spray into the pot. stops the risk of drift and only gets the weed.

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Thank you nickyt08, it looks as though i have a long job ahead of me. I wouldn't mind so much if my soil was easy to handle but being clay it's rock hard at the moment. How I envy people with friable soil!!. never mind, it gives me something to do and is a challenge.