thank you. If there is nothing in the lease as regards ***** ***** in this respect as you say, then your father will need to consider falling back on his so-called prescriptive right under the prescription act to continue to exercise a right of way in this regard.
In order to claim a right under the prescription act, he must be able to show that for a continuous period of 20 years or more, he has exercise the right of way over a given area to access his garden and without permission, payment or secrecy of the landowner.
Providing he can demonstrate all of these elements, then he can consider swearing statutory declaration as regards ***** ***** he has exercised and then subsequently applying to register this as a formal right as against the landowner's title. Naturally, the landowner can dispute any statement made and where possible, if he is able to obtain statements from other individuals who may be able to provide corroborating statements or alternatively, where he has any other evidence in support of his claims though I suspect this may be unlikely, such supporting evidence can be helpful if the landowner brings a dispute to the property tribunal in this regard.
However, one thing that is presumably in your father's interests is that he can show that he has been demised the garden and by extension, it will not be a difficult argument to make that he has actually accessed the garden in practice and from what you say, this is only possible in one particular way.