26. In this Part, “non-residential premises” do not include—
(a)premises due to be converted to a dwelling-house by the time the sale of the property interest is complete; or
(b)a dwelling-house or a building ancillary to a dwelling-house used for either or both of the following purposes—
(i)letting under a lease(1); or
(ii)home working.
In this case, “lease” does not only mean a long lease - see regulation 3(1).