Driving while unfit through drink or drugs
This is a similar offence to driving with excess alcohol. The difference between the two is that, to be charged with driving with excess alcohol, a specimen declaring you over the drink drive limit is required. If they do not have a specimen, for whatever reason, they can simply charge you with driving while unfit under the influence of drink or drugs and the prosecution would centre around a doctor's or police officer’s opinion of your suitability to drive.
What are the punishments?
You could face a driving disqualification, six months imprisonment and a £5,000 fine.