If you primary concern is to terminate the contract then you can only do so if the landlord has committed a repudiatory breach of contract. This means a breach which is so serious that it does to the root of the contract and denies you all, or substantially all, of the benefit of it - it effectively means that the landlord has not provided you with accommodation fit for human habitation.
Minor repairs do not fall in to this category, but issues of damp can do. You should contact the enviro health dept. of the local authority and ask them to make an inspection. If they make a declaration that the property is unfit for human habitation then you should ask for this in writing from them. You could then terminate on the strength of this breach.
If the enviro officer does not find the property unfit then you have a right to ask that the disrepair (including cleaning) is remedied.
You should formally write to the the landlord 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 you 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 you can issue a claim for the money yourself through Her Majesty Courts Service's online service: http://www.moneyclaim.gov.uk/
Its pretty cheap and straightforward to use
If this has been useful please kindly click accept so that I may be rewarded for my efforts. It will be gratefully received and you will be free to ask follow up questions.