My hubby is on Celexa and has just gotten the generic one called Citalopram. It is much less expensive. You might check it out. If you get the pills what about taking 1/2 the dose for awhile. You shouldn't just get off of it cold turkey.
Another idea. I don't know if they have this in England but here we have Patient Assistance Programs from the drug companies. I got my sister on the one for Lilly for her Prozac and she gets it free. You have to be low income and fill out some paperwork and get your doc to send it in. If you need more info I could get it for you.
Also some docs have samples to give away free. You might check that out. Check with your doc and tell him you have no money to get your pills and see if he can help you. He surely won't want you going cold turkey.