Police powers to enter your property in connection with drink driving come from section 6E of the Road Traffic Act 1988
(1) A constable may enter any place (using reasonable force if necessary) for the purpose of –
(a) imposing a requirement by virtue of section 6(5) following an accident in a case where the constable reasonably suspects that the accident involved injury of any person, or
(b) arresting a person under section 6D following an accident in a case where the constable reasonably suspects that the accident involved injury of any person.
Save in the circumstances above the police do not have powers to enter your premises to perform a preliminary test. In the case of Fox v Gwent Chief Constable the conviction for refusing to provide a preliminary test was set aside where the police entered the motorist’s home as trespassers. Interestingly though after he was taken to the police station and provided a sample which was over the limit the court allowed that conviction to stand. This only applies to private property, where a motorist simply moved off the road onto a private forecourt and the court said that the motorist had an obligation to comply with the request.
The case of Morris v Beardmore made it clear that the police officers cannot enter a private property if the owner forbids them to. The owner has to make it clear that the police are not allowed on the property, The case of Snook v Mannion  R.T.R. 321 made it clear that it is not sufficient to shout abuse at them and tell them to ‘Fuck off’. It needs to be made clear that they are not allowed to enter the property. The driver only gets protection in a place where he is not a trespasser, so he cannot run into a property as a trespasser and say that the police are also trespassers.
Where there has been an accident the police are entitled to enter private premises if they reasonably believe that there has been injury to a person. If this is the case then they can force entry if necessary to secure a preliminary test or to arrest.
If you think that the police have entered your premises unlawfully in relation to a drink driving matter you will need expert drink driving solicitors to assist.
For free initial advice in relation to any drink driving matter call us on 01623 600645