If there is no express covenant the Common law will imply for the Landlord to provide for quiet enjoyment of the premises as fred, who is very knowledgeable on such matters, says. If there is a breach of this covenant you may have a remedy against the Landlord. Consult a solicitor with full information and ask them to write to the Landlord regarding this implied or express covenant reminding them of their responsibilities, if the action by others is criminal as Eddie says go to the police.