Hi Barry
I've just enquired with Natural England about the use of Larsen traps and wether I need a licence for magpies. I don't, but must - and to quote "You should read the licence carefully to ensure you adhere to its conditions"
Here's the link they sent me (I think you'll have to copy and paste it):
http://www.naturalengland.org.uk/Images/wlc-gl04_tcm6-24149.pdf
Take particular notice of paragraph 1 - the purposes of control and also the welfare of the decoy bird.
Hope this helps.
G.