User xngtng's answer already answers the question, but to add a little more detail:
The full list of grounds appears in Schedule 2 to the Housing Act 1988. The Schedule's title is "Grounds for Possession of Dwelling-houses let on Assured Tenancies".
Most of the rules associated with those grounds are contained in section 7 of the Act ("Orders for possession") and the eponymous section 8 ("Notice of proceedings for possession"). Sections 8A, 9, 9A, 10A, 11 and 12 add further details relating to particular grounds, and there are occasional references to the Schedule elsewhere in the Act too.