Q. I rent a flat to a tenant who is in rent arrears. She hasn't been seen for weeks and I can only assume that she has decided to move on. The tenancy contains a clause entitling me to bring the lease to an end for non-payment of rent. Can I enter the flat and change the locks?
A. It is a criminal offence to re-enter and terminate a residential tenancy (which is known as "forfeiture") where a tenant is in lawful occupation. There is, however, an exception to this rule. Where you have a reasonable belief that your tenant has stopped occupying the premises for the purpose of her residence, forfeiture is permitted (though you must first send her a notice requiring payment of the rent due).
A temporary absence from the property will not be sufficient to satisfy this exception. Your tenant could simply be on holiday or staying with friends/family and if that were so, if you were to change the locks, you would find yourself liable for substantial damages for unlawful eviction upon her return. Given the potential criminal sanctions which can follow, it would be more prudent to issue court proceedings to end the tenancy upon the basis of her rent arrears.
