Thanks for your reply.
If they have been granted a tenancy of the entire house then they have an exclusive right to occupy the entire house and the landlord cannot simply move back in to the spare room.
In respect of the disrepair, they have a right to a property in repair and can enforce this against the landlord.
They should formally write to the the landlord (copying in the agent) specifying the disrepair, making a list of the reasonable repair required and ask that he make those repairs within a reasonable time (eg. 14 days). State that if the landlord does not make the repair within that time they will pay to have the repairs made and will seek to claim the expense from him and are prepared to make an application to court if necessary.
If the landlord does not make the repair you can pay to have it done and then write formally to him requesting the payment of the cost, again within a reasonable time). If he does not pay they can issue a claim for the money yourself through Her Majesty Courts Service's online service: http://www.moneyclaim.gov.uk/. Write to them first asking for the money and stating that you will issue a claim if it is not received.
Its pretty cheap and straightforward to use.
The landlord does not sound as if he is particularly aware of the law. If they have paid a deposit and are occupying the premises under an assured shorthold tenancy agreement then the landlord should have placed their deposit in a tenancy deposit scheme and provided them with details of the scheme/deposits reference. If he has not done this then they can sue him for the return of the deposit and a fine payable of three times the deposit amount from the landlord to them.
Open a file, send letters by registered post, keep copies of everything for use in any claim you may choose to issue at a later date.
The tenancy agreement will likely state the terms of visitations, but if he is doing this in breach then there is little practically they can do because they have not suffered any financial loss as a result of this. Put it in the letter and this may prompt his compliance.
I've got to go out for a couple of hours now (unexpectedly). If you have further questions I will be able to reply upon my return.
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