This might help if you haven't already seen it:
http://www.disabilityrightsuk.org/perso ... ayment-pip
I'd also try to get the Citizens Advice Bureau to help, if you can.
I'd expect a lot of resistance to your claim. I tried to get DLA and failed - in hindsight my mistake was probably not realising that they don't take into account anything that isn't backed up by a statement from the Great And Good, so get your diagnostician / doctor to write down everything that your case depends on. Expect to be turned down initially, be prepared to go to appeal, and expect it to be somewhat stressful.
Another of my own problems with these claims is that I'm useless with face-to-face conversation. I always tell them that and ask for everything to be done by letter and email, but they usually ignore it and phone me up or expect to talk face-to-face. It might be worth really digging your heels in about that, if you're anything like me, and if the rules absolutely insist on face-to-face, then try to get an advocate to accompany you, if you can find a good one.
Oh, and expect it to take them a long time. Don't know if you saw this:
http://www.theguardian.com/society/2015 ... s-scrutiny
Hopefully the gov have responded to the outcry by now and got the waiting times down a bit, but I wouldn't count on it, knowing their reluctance to spend money.