Driving (see driver) while affected by alcohol. Drunken driving covers two separate legal offences.(1) Driving while unfit. It is an offence to drive or attempt to drive a motor vehicle on a road or public place when one's ability to drive properly is impaired by alcohol or drugs. Drugs include medicines (such as insulin for diabetics), and the offence appears to be one of strict liability. It is also an offence to be in charge of a motor vehicle on a road or in a public place while unfit to drive because of drink or drugs, but the defendant will be acquitted if he can show that there was no likelihood of his driving the vehicle in this condition (for example, if he arranged for someone else to drive him if he became drunk). A police officer can arrest without a warrant anyone whom he reasonably suspects is committing or has been committing either of these offences; he may also (except in Scotland) enter any place where he believes the suspect to be, using force if necessary.(2) Driving over the prescribed limit. It is an offence to drive or attempt to drive a motor vehicle on a road or in a public place if the level of alcohol in one's breath, blood, or urine is above the specified prescribed limit (35 micrograms of alcohol in 100 millilitres (ml) of breath; 80 milligrams (mg) of alcohol in 100 ml of blood; 107 mg of alcohol in 100 ml of urine: Road Traffic Act 1988 s 11). It is also an offence to be in charge of a motor vehicle on a road or in a public place when the proportion of alcohol is more than the prescribed limit, subject to the same defence as in being in charge while unfit. Both these offences are offences of strict liability: it is therefore not a defence to show that one did not know that the drink was alcoholic or that it exceeded the prescribed limit. The normal way in which offences involving excess alcohol levels are proved is by taking a specimen of breath for laboratory analysis, but this is not necessary if the offence can be proved in some other way (for example, by evidence of how much a person drank before driving). There is no power to arrest a person on suspicion of committing or having committed an offence of this sort before administering a preliminary breath test.Most charges involving drinking and driving are brought under the offence of driving over the prescribed limit rather than driving while unfit, but the powers to administer a breath test or to take a specimen of breath for analysis apply to both offences. The penalties for either of these offences are a fine and/or imprisonment, endorsement, and obligatory disqualification (in cases of driving or attempting to drive) or discretionary disqualification (in cases of being in charge). Under the totting-up system, the discretionary disqualification offences carry 10 penalty points and the compulsory disqualification offences carry 3–11 penalty points (which are only imposed if there are special reasons preventing disqualification). See also causing death by careless driving when under the influence of drink or drugs; offences relating to road traffic.