How to make the move from theatre into TV and film work
Surprisingly easy to do.
Two steps: register with an extras' agency - they won't charge a fee if they are bona fide, check out their client list to ascertain this. If they are listing major soaps like BBC Casualty, EastEnders, Dr Who, Upstairs Downstairs then they are the real deal.
Secondly, apply to adverts for unpaid student films. Do a crackingly good job and then you've got showreel experience. Once you've got the unpaid film experience (and you don't have to specify that it is unpaid either) then the paid film work will follow. Extras agencies will actually pay you good money anyway even though student films usually only pay expenses.
I've got into a number of feature films by having the student films listed on my CV - so I know it works and I am now not doing student films but am working on a big screen film. It really is a case of doing the boring extra work/getting that good student film role and doing it well. It isn't impossible, it just requires perseverance.
Good luck with it.