can the police legally take my admission to a car crash when I am in a state of shock in the middle of a car crash? and if not under what act?
You don't give much in the way of specifics, but it sounds like you confessed something to the police at the side of the road immediately after the accident, and now wish to dispute that confession. If you are taken to court and the police want to introduce your confession as evidence then you (through your lawyer) can ask the court to rule it out.
You may be able to do so on a number of grounds.
Was the confession properly recorded at the time?
Were you treated in an oppressive manner, such that you felt you had to say what the police wanted to hear.
Did you think you might get more favourable treatment if you said what the police wanted? For instance, did you think you might be allowed to go home once they were satisfied?
Were you given a proper rest, or were you in a mental state that might cause you to say things without understanding the consequences (it sounds like this would be your main argument, but consider the others too). [Edit] If you needed medical treatment that would also be relevant.
Were you properly cautioned (that speech beginning "You do not have to say anything...") before the police asked you questions.
If you think you may be facing criminal charges then you should get yourself a lawyer sooner rather than later. A lawyer will know all about this and be able to navigate the relevant legal processes on your behalf.
A bit of background: back in the 1970s the police frequently attributed incriminating statements to suspects when arrested, such as "Its a fair cop, guv", or "Who ratted on us?". The rules in PACE were made to stop such "verballing".