Occupying a property without the owner’s consent is technically known as squatting, but you as landlord cannot use force to effect an eviction without yourself committing a crime.
However, waiting until the property is unoccupied and then changing locks - peaceable re-entry - is not a crime either, though you are obliged to take care of belongings.
Trespassing is where there is foced entry to the premises and is is a crime. Where there are signs of recent forced entry, landlords can seek police assistance to evict trespassers.
Fortunately, in the case of squatters, it is quite straightforward for owners to evict legally if they follow the correct procedures.
The owner will need to apply to the local County Court or the High Court for a possession order using the special procedure for squatters. You don’t need to know the name of the squatters to use this procedure.
If you can show that the occupiers are squatters (by proving your own title) you should receive a possession order within a couple of weeks. This may be delayed further, depending on if the occupiers defend their position or ask for more time to find alternative accommodation.
If the occupiers refuse to leave voluntarily once you have the order, you will need to use the court bailiffs, which may cause a further delay.
The Criminal Justice Act 1994 introduced an even faster procedure which allows landlords to serve a Notice of Possession on squatters of less than 28 days, which should result in an Interim Possession Order from the Courts. This gives trespassers just 24 hours to leave or face arrest.
Where squatters (trespassers) displace rightful occupiers (occupying tenants or owners) they commit a criminal offense if they stay when asked to leave. In this case rightful occupiers (not landlords) must present the trespasser with a sworn statement that they are the rightful occupier, on in the case of tenants, a statement from their landlord.
In normal squatting situations the police will normally refuse to assist as there is no crime – it’s a civil matter. In the latter case the police may be willing to assist as the occupiers are committing a crime.