Page 303 of the Laidler book has a picture of one in the MOD pattern room. The quality of that one is much better than this one. It appears to at least have real Sterling trigger, grip and bolt parts. I think the Imperial War Museum in London also has one of the IRA copies of a Sterling on display if you ever get there.
Here are some funny pictures of some crude IRA guns that are similar to this one...
htt p://amodestpublication.wordpress.com/2009/05/08/loyalist-paramilitary-improvised-machine-guns/
Also interesting the some IRA gunsmiths stamped serial numbers like this one has if that what it is.