GymBum
It's not murder because they don't get into the car with the intention of killing a person or causing them GBH (that is the intent needed for murder). They get into a car believing they will drive home safely.
However, it may be manslaughter but it is complex
CPS guidelines are:-
"If the vehicle was intentionally used as a weapon to kill or commit grievous bodily harm, a charge of murder may be considered. If the killing was involuntary, that is to say, where it was not intended, manslaughter may be considered. Manslaughter may arise as unlawful act manslaughter and gross negligence manslaughter. In addition, the charge of corporate manslaughter is also available.
Manslaughter is an obligatorily disqualifiable offence - Part II of Schedule 2 of the Road Traffic Offenders Act 1988 (RTOA 1988). An extended retest is also mandatory (section 36 of the RTOA 1988).
Manslaughter should also be considered where the driving has occurred "off road" i.e. other than on a road or other public place, or when the vehicle driven was not mechanically propelled, and death has been caused. In these cases the statutory offences such as causing death by dangerous driving or causing death by careless driving do not apply.
Prosecutors should also see the chapter on Homicide: Murder and Manslaughter in our Legal Guidance.
Unlawful act manslaughter
It must be proved that:
The suspects act caused the death of another;
The suspects act constituted a criminal offence in itself;
The suspect had the mens rea appropriate to the unlawful act which caused the death of another; and
The suspects unlawful act is objectively recognised as subjecting another to the risk of some physical harm, albeit not necessarily serious harm.
Unlawful act manslaughter will be the most appropriate charge when there is evidence that a vehicle was used as an instrument of attack or to cause fright, (but where the necessary intent for murder is absent), and death occurs as a result.
In the context of driving offences, it is important to remember that there is a difference between cases where there is a specific unlawful act which relates to the manner and standard of the driving, and those where a death has occurred as a result of driving that is unlawful only because of the negligent manner of its performance.
Driving carelessly or driving dangerously do not, on their own, amount to unlawful acts for the purpose of unlawful act manslaughter. Andrews v DPP [1937] A.C. 576
Unlawful act manslaughter should, therefore, only be charged instead of causing death by dangerous driving where there is evidence that the driver either intended to cause injury to the victim or was reckless as to whether injury would be caused. "
www.cps.gov.uk/legal/p_to_r/road_traffic_offences_guidance_on_prosecuting_cases_of_bad_driving/