If the amount of arrears is less than £10,000 you can issue proceedings against the tenant in the Small Claims Court. If the tenant admits the claim there will be no hearing. However, if they do not there will be a court hearing and the matter will be dealt with by way of negotiation.
If the amount of arrears is more than £10,000 you must issue proceedings in the County Court. It is advisable to seek the appropriate legal advice from a solicitor or the Citizens Advice Bureau. The failure to pay rent does not give the landlord an automatic right to evict the tenant. If the correct procedures are not followed, then the landlord may be liable for harassing or illegally evicting the tenant, please see the related question for the proper procedure for eviction.