The Police and other emergency vehicles have no special dispensation in Road Traffic Law.
However.................................................
In an emergency they can get from A to B in ANY way possible. In theory this does NOT have to be safe in law (there own service contract will say something different) but if anything happens then they will have no special case in court.
Police Officers and Paramedics etc are often taken to court for dangerous driving etc. Marked vehicles have even had parking tickets.
One can argue they are actually treated less fair at court as they are deemed professional drivers and should have known better.
The few things which a subsection applies is the seatbelt rule (if transporting people, i.e safety issues), the use of telecommunications equipment (i.e walkie talkie) under the new mobile phone rules and the use of air horns.
There is also a bog standard defence to almost any law, in the act (i.e the driving) was deemed necessary to save life and limb. But again, if something happens it will be on there shoulders.
Under the fairly recent Police Reformation Act, the onus for traffic offences was taken away from the Chief Constable and was given to the actual driver. Therefore you will no longer see R vrs The Chief Constable at court.
Finally, though only one case exists in history, traffic laws can be legally broken by a Police Officer in uniform. They will take precedence, say, at directing traffic at traffic lights. You follow them, not the sequence on the lights for example.
A police passenger directed the driver to go through a red light and the driver hit somebody. At court, the driver stated he was following the directions of a uniformed Police Officer!!!!!!!!!!!!!!!!!!1 I doubt they were best friends in the canteen!!