I'm currently awaiting my date date for the West Mercia Constabulary as a Student Police Officer (Bobby basically). 36 weeks training, then a full constable.
The process which I went through is up to a 2 year process: You have an application sift which is 10 questions, the first 4 broken down in sub questions, then a further 6 questions which are based around "Why do you want to be in the Police Force" and those type of questions. A long with you supplying your personal details (name, address, age, family details, schooling and such).
Providing you pass that, you get sent to an offsite Assessment Centre (My one was in Derby). Where you have two/three written notes / letters in response to a customer service enquiry based upon a fabrication of a shopping centre. (The whole day is based around this shopping centre). Also, you have a verbal interview, in which they ask you around the questions which you first submitted (so keep a record) though, first time around they asked the exact same questions, second time they threw in a couple of random ones. So bear that in mind. If you revise the key compentancies you won't have a problem. As the whole Assessment centre is based around these. You are given a list of these to look through and what exactly each of them are, with good or bad examples. You also have a numerical and logic based quiz (mulitple choice) and the part which most find the hardest: The Roleplay. 8 Rooms, lasting 5 minutes each (5 minutes prep in one room, bell goes, stand outside for 90 seconds, bell rings again, go into the roleplay room, bell rings standoutside prep room and so forth until you have done 4 face to face Roleplay interactions). You will be faced by actors, but not actors in the normal sense. They are all scripted so can't offer you any more infromation than their 10 or so lines in which they have learnt. If at any point you stop talking, they will lower their head so you will be looking at the top of their head, which is surprisingly offputting. You have someone else in the room who is away from your line of sight, who is marking you and noting when you hit these key lines and how you put your self across. If you remember the 5 key questions (Taught to me as the 5 W's) then you can't go far wrong. There will be the odd surprise though... West Mercia as of last year required a 60% overal mark for a pass and for you not to get a 'D' in any part of the Respect for Race / Diversity competency.
After that, you have a Physical, which for West Mercia is a bleep test (West Midlands and other forces do an assault course), which you require 5.5 to pass and if I'm honest... 5.5 is such an easy level you'd really struggle not to pass. Also, a push and a pull fitness test which requires you to move 35kg worth of dyno (again very easy), the 35kg level is over an average of 5 attempts I believe.
You then have a medical, which tests your lung capacity, your hearing, your sight, heart, abdomen, a check for diabetes (and other basic wee tests - though not drug tests as this is a seperate day, usually before the physical), relex test, blood pressure and other small tests. Nothing serious there either.
During all of that you are being veto'd and security assessed (your family get looked into, as well as your self to make sure you are suitable) and then you get a start date (West Midlands have two intakes per year, if you miss one you then have to wait circa 6 months for the other intake). Also your two personal references would be contacted, as well as your last employers within the last 5 years (could be 10 actually coem to think of it).
Each force varies, but that's the procedure I went through to get to where I am at the moment (awaiting start date).
Any specific questions which I can answer, then feel free to fire away Burnsy. I won't be able to answer them all as we'd be in different forces and therefore different ways of doing things, but I am more than happy to offer my opinions and if I have done something similar, to help you out.
My email is in trust for any thing else which you want to take off board.
For West Merica, there are no interviews with the superior ranks, nothing like that. Also, before you even get an application form, you have to attend an open day, where you get to speak to Police Officers (some specialized ones too), listen to a couple of talks and watch a video. They want to know that this is what you want to do, before they consider you. This is why it's such a long period of time before you join (in my opinion), as it really does weed the people who think... why not give it a go, and the people who really want to be a part of it. 2 years is a long time.
my drink driving has a 10 year probation (correct word?) time and won't be accepted until that clears. So currently losing my weight to go back into the Army (left 06 after 4 years) 
about a stone left to lose then I can start my re-application 
.
