INTM153310 - Description of double taxation agreements: Termination
An agreement is to remain in force until terminated by either party who can do so by giving written notice. It then terminates for any year of assessment (or financial year) beginning on or after 6 April (or 1 April) in the calendar year after the one in which the notice of termination is given.
Normally the Article provides that an agreement cannot be terminated until after a specified number of years from the date of entry into force.