As a general rule, break clauses are best avoided as they are prone to misinterpretation and often ineffective when the landlord tries to enforce them.
For that reason we do not include example wording here. Instead, it is recommended that your AST have a relatively short minimum term of six months.
After that, your tenancy can continue to roll on monthly, allowing both parties to terminate the agreement by serving appropriate notice (2 months for landlords and 1 month for a tenant) as set out in the agreement.
If you want to add a break clause into your agreement you would need the wording to be created by a solicitor as it has to be very specific.