Regulations for outside a commercial building's Fire Exit?

I've been searching the internet but I can't find this anywhere:  How much space is required outside a commercial building's fire escape? I rent a small field for a couple of ponies next to some commercial units and there's a distinct lack of knowledge on whether the owner of the land is able to rent the area to me for my ponies at the same time as renting the unit out to someone else with an emergency exit leading out on it.

I of course, feel the exits should be used in case of emergency only, however the new tenants use them for their convenience, taking their lunch breaks out in my pony's field, leaving the fire exits open most of the time and today, putting a couple of trestles out with a big chunk of freshly painted metal on to dry.

Are there any regulations saying how much space needs to be available and whether it needs to be generally accessible for non emergency use i.e. included in the lease or not?