If that's all the break clause says then you can serve a notice at any time after four months from the commencement date of the tenancy, specifying any date for the termination of the tenancy, provided that the date of termination is at least two months after the date of service - i.e. two months after the date when the landlord or his/her/its agent receives the notice. Bear in mind, however, that if you exercise the break clause during a rental period (i.e. if rent is payable on the 29th of each month, on any day other than the 28th) then you'll be liable for the whole month's rent and you won't get a refund for any part of the month after the lease is terminated.
And the use of the word determine isn't a typo or a mistake. In law, the word determine is synonymous with terminate. It's perfectly proper to say that a tenancy has been determined, meaning that it's come to an end.
If that's all the break clause says then you can serve a notice at any time after four months from the commencement date of the tenancy, specifying any date for the termination of the tenancy, provided that the date of termination is at least two months after the date of service - i.e. two months after the date when the landlord or his/her/its agent receives the notice. Bear in mind, however, that if you exercise the break clause during a rental period (i.e. if rent is payable on the 29th of each month, on any day other than the 28th) then you'll be liable for the whole month's rent and you won't get a refund for any part of the month after the lease is terminated.
And the use of the word determine isn't a typo or a mistake. In law, the word determine is synonymous with terminate. It's perfectly proper to say that a tenancy has been determined, meaning that it's come to an end.