I'm sorry that your life is so bad that you'd want to end it. Of course if you feel like ending your life and have had 2 failed suicide attempts you should be in hospital if that's what you need. I can understand why they took your antidepressants off you - they did that to me as well, took me a long time to get my meds all back in my control. The option is there for dad to take care of them and I mean carry them in his pocket and sleep with them under his pillow and watch you take them every day. It's worth a shot but in future don't take meds you really need as od's.
I'm also in the UK but in a major city that has a large psych hospital. We have a children's and young people's unit where our kids all go or get outpatients help. Kids can be admitted with the authority of 1 psych and a parent. Are you saying that dad will not agree at all in any way for this to happen? If so why would he refuse this help? Is there a mum anywhere who could do this instead?
At the end of the day your dad is going to know that you are in hospital so there is no way of avoiding his upset over the event. Why do you think the psych will say no? Has he said so before? If you would need to go into a serious ward or a ward of adults then I'd agree that almost anything is better than that. Being with people who have much more serious disorders is not good for any kid your age. People who are very psychotic or schizophrenic can be very scary even for those of us longer in the tooth who've been there before. Go in with depression and come out with schizophrenia!
Is there any suggestion of you having borderline personality disorder rather than depression or as well as? I can see them keeping you as far away as possible from the ward in that case. It's in your best interests I assure you.
If you are determined your dad won't be able to stop you going in so you may as well set off in the morning for the A&E and insist they keep you.
I do just wonder however if it may help to tell us the complicated and nasty issues in your life that have driven you to this stage where death seems preferable? I am absolutely certain nothing is worth that at age 15. Things improve, they change, you'll feel less depressed one day, no one has suicidal depression for year and years, it is treatable and people recover. The way I felt in my teens is a world away from the one in my 20's. I've qualified, got married, had kids, had a good career, made lots of friends and I'm treating other mentally ill people myself now.
Send me an emil if you want to talk to me.