It was the definition in the policy that applies to members as employers. It is quite broad already so it includes locations in situations including business travel, conferences, and work-related social gatherings where House of Commons-related activities are performed and where inappropriate behaviour or comments might reasonably be perceived to have a subsequent impact on work relationships, environment, or performance. To me that is already a very broad definition in general for relationships that are truly personal, truly private, and completely outside of any connection to parliamentary functions.
The ordinary law would usually apply to those relationships; certainly, the criminal law, if any criminal activity were to take place. As you get into the completely personal realm it becomes more difficult for the House to regulate that behaviour. At the same time the behaviour that could be regulated as being connected to parliamentary activities is quite broad because you engage in so many activities that are in some way connected to parliamentary or party functions.