Good morning! 

I would like to ask for advice. Our company is on the industrial estate. We have couple of 'neighbours' companies' between our units. We have designed smoking area. The other companies (much smaller than our) do not have it! Employees from the other companies smoke near our building.

Last time I saw the person, who litterally smoked at the front of our Fire Exit door! The additional problem is caused by short, public road, which divide our units.  

Can I ask other than our employee do not smoke in other than designed area? Or I do not have a right as there are not our employees?

I would be really grateful for help.

You can make suggestion but as a public place you would be unable to insist.

Try a friendly chat with the owner/manager of these other firms proposing how more professional staff would look using a designated area

A double edged issue. On the one hand, if you have a designated smoking area, does this provide some shelter, if so other people might prefer to use it rather than standing out in the open. On the other hand, smoking areas tend to be social areas as well, where employees can chat to other employees, often ones they wouldn't normally get to speak to. Do you want people from other companies evesdropping on such conversations?