Probation in criminal law is a period of supervision over an offender, ordered by a court instead of serving time in prison. In some jurisdictions, the term probation only applies to community sentences (alternatives to incarceration), such as suspended sentences.
When your landlord changes your door locks because you are behind on paying the rent, the landlord must give you advanced written notice of the proposed lock change AND a written notice at the time your locks are changed.
If you go in and change the locks before your tenants have moved out voluntarily (HOWEVER badly they are behaving) this will put you in breach of the Protection from Eviction Act 1977. You will be vulnerable not only to prosecution but also to a claim for financial compensation from your tenants.