Weasel

we were down on our allotment until late last night, 10 pm or so, watering, weeding and burning the dreaded Marestail. About 9 o'clock our dog jumped up and started frantically pacing the fence between us and the slightly but pleasantly overgrown plot the otherside. We could see the long grass moving as something made it's way through, eventually a small brown head popped up, which I identified as a Weasel, I suspect it may have a nest? in the compost heap. Delighted to see it, however I have to trust that it will leave our hens in peace, I've seen a few mice and rats on the field so hope it continues to hunt them. I don't think the Weasel poses a threat to full grown hens unless anyone knows different? ( ps our run is rat proof and has 1/2" weld mesh)

are you sure it was a weasel and not a stoat?
Take a look at this - but yes they are a threat to chickens  

http://www.wildlifebritain.com/stoatorweasel.php

Have seen a rabbit taken down by a weasel (no black tip)  

because they pose a threat to his chickens now, if it becomes a problem that means the weasel/stoat has already acted and the chickens will be dead  . They like the foxes will be breeding now and have lots of hungry mouths to feed.

thanks for your replies, definitely a Weasel but I couldn't bring myself to kill them, trusting they wiil do more good than harm I.e. killing rats and mice, if they start killing the hens  then I will have to take action. Also haven't heard of any fellow chicken keepers losing hens as yet !