I couldn't be sure but I think the flower could be prunella vulgaris in its early stages, also known as selfheal.
You'll ask what I know about such things. I am at University. I am a lab tech there and am currently researching pentacyclic triterpenes (of which PV is choc-a-bloc). I hope to use them in my research project since they may help to inhibit the slight gastric bleeding that my last batch of E's seemed to trigger
The picture is a little indistinct. If the leaves are pointed ovals it may be P.V.
Is there a reward?
There was to be a reward, but I'm sorry to announce that Pizza on the Trot is not with us any more, Mr Grimes and the staff will be sadly missed. They were hit in crossfire overnight. Our non-roving reporter has been ordered to take another picture of the mystery weed, and with any luck should arrive back safe and sound shortly.