A purchaser has noticed that there is a pathway at the back of the property (covered by a fence) that is actually a driveway to another property (vendor's primary residence), they would like to make use of this as it is a shortcut to a local walkway. Legally how does one go about this?

The purchaser should contact the estate agent and raise the question with them in the first instance.  If the Vendor is the owner of the adjoining property, the estate agent could relay the purchaser's request for a right of way to travel by foot from the rear of the property in sale over the driveway to the rear of the property down to (name the road to be precise).  If the decision is yes, the exact agreement should be in writing.  For example: If an engineer's report show that planning has been granted for an apartment block on the lands to the rear of the property, a solicitor would recommend that any right of way be recorded in writing for future use.

The information shared on this site is meant to be helpful but you should always speak to a solicitor directly as additional details about your agreement or situation may change the answer.