The Police Federation highlighted legal advice which indicates that pursuits and emergency response situations are likely to leave officers at risk of prosecution for careless or dangerous driving.
Ministers faced calls to change the law to give greater legal protection to emergency services drivers.
Tim Rogers, the Police Federation of England and Wales' (PFEW) lead on roads policing, said: "Legal advice has recently highlighted that police response and pursuit drives are, in most circumstances, highly likely to fall within the definitions of careless and or dangerous driving.
"The federation has raised this matter with numerous MPs but to date the difficulties remain with our proposed draft for legislative change not yet having been progressed to a point where officers are appropriately protected."
In a letter sent to forces in England and Wales, Mr Rogers advised officers "not to undertake any manoeuvre which may well fall outside the standard of the careful and competent non-police driver".
He said: "There are no exemptions to the offences of careless or dangerous driving to permit emergency driving.
"This matter has been considered by chief constable Anthony Bangham, NPCC (National Police Chiefs Council) lead for roads policing. He accepts that, at least as far as pursuits are concerned, drives are highly likely to fall outside the law as it is currently drafted."
A "typical" response or pursuit drive is likely to involve the officer contravening traffic signs and/or speed limits, he said.
The legal advice suggests that while emergency services can disapply traffic signs and speed limits, there are no exemptions to the "very wide" definitions of careless or dangerous driving.
Mr Rogers said any driving in emergency situations was therefore "likely to be unlawful, placing the driver at risk of prosecution and proceedings for gross misconduct".
Mr Rogers said the Independent Police Complaints Commission recently directed a force to bring proceedings against an officer for gross misconduct for careless driving, adding: "Gross misconduct is conduct that would justify dismissal."
The PFEW has raised the issue with MPs including Home Secretary Amber Rudd and Policing Minister Nick Hurd, pressing for a change in the law.
"To date, the difficulties remain with our proposed draft for legislative change not yet having been progressed to a point where officers are appropriately protected," Mr Rogers said.
A Home Office spokesman said: "All emergency services, including the police, are exempt from speed limit, traffic light and sign violations when undertaking an emergency service response.
"However, they remain subject to the general law on motoring in the same way as members of the public - including the law on careless and dangerous driving.
"Decisions on the management of pursuits and response driving are an operational matter for forces."