Where are all these flies coming from?

Over the past 3 days I have been chasing flies out of the house.  Warmer weather I thought, but they all seemed to be the same kind and size!  Just seen another one on the landing and then it clicked they must have escaped when I stored some maggots in the under stairs cupboard for the hens!    

 

It was my fault, I couldn't find the maggot tub (didn't feel like dimantling the garage to find it)!  Put them in a tub with cling film over and holes poked in.  I did notice some had wriggled to the underneath of the tub but thought I had caught them in time, obviously not. 

The flies have seemed a bit dozy which is one consolation as they were easy to catch and let out of the window.  Hopefully they will end up as food for the many nesting birds.  Now where did I put that maggot tub?!!   

If they are not your escapee maggots they could be these, http://en.wikipedia.org/wiki/Cluster_fly

They are never very fast when they come out of hibernation.

No they were definitely the maggots, plain old blue/green bottles.  Think they have all gone now and hubby didn't even notice!!