Ending a joint tenancy can sometimes be more complicated than ending a sole tenancy. Case law has confirmed that one joint tenant can serve a notice to end the whole joint tenancy (i.e. one tenant can end on behalf of both tenants). But for that to be possible, either all legal requirements, such as how the notice is given and the notice period, have to be strictly complied with, or all parties (the landlord and both joint tenants) need to agree to depart from the strict legal requirements. 

Additionally, a sole tenancy can be ended by what is referred to as 'surrender by operation of law' (also referred to as implied surrender), whereby the tenant doesn't give a written notice to end the tenancy but their conduct is such that is is clear he or she has given up the tenancy e.g. removed all belonging, vacated it and returned the keys to the landlord. A landlord has to accept an implied surrender for it to be effective. 

Often, when a sole tenant on a social tenancy (such as a secure tenancy with a local authority or an assured or assured shorthold tenancy with a social housing provider like a housing association) leaves a property and signs a new social tenancy agreement, that is considered to be a surrender by operation of law because you cannot legally hold two social tenancies. 

In the recent case of Westminster v Kazam & Anor, the court considered how an implied surrender might work in the case of a joint tenancy. Here, one joint tenant (A) had left the property and obtained a new social tenancy. However, the court found that the other joint tenant (B) has not behaved in a way so as to accept A's behaviour as a surrender nor behaved in a way as to accept the whole tenancy has been ended. It concluded that all joint tenants must be behaving in a way as to amount to surrender, not just one on behalf of both - unless there is express authority from one joint tenant for one other joint tenant's behaviour to amount to a surrender.

This may appear to be contrary to the position that one joint tenant can end the whole tenancy by serving a notice. But remember that where one joint tenant serves notice to end the whole tenancy, all legal and technical requirements of that notice have to be met or waived by all parties - landlord AND the other joint tenant. So it follows that for the joint tenant to be ended by an implied surrender,  i.e. where a valid notice hasn't been served, all parties must accept it.

An intentionally high threshold has been set as to whether a joint tenancy can be ended by implied surrender. This case helps to protect the position of joint tenants left behind in a property when one joint tenant leaves. Unless the remaining party agrees to the surrender, or one of the joint tenants serves a valid notice, the tenancy remains intact and the remaining party can continue to live there.