I am currently employing a Tunisian man who is married to a English woman. They have been married for approximately one year and are currently going through marital problems. If they were to separate/divorce how does he legally stand to stay in England and is their anything he can do to remain in England?

What is a planned marriage for him to stay in the UK?
Tricky one.

I personally wouldn't risk it as I'm not 100% sure but if they were to divorce then that no longer means he can reside in the UK.

Do u know if he has all the rights, work permits and VISA's to stay in UK?
What Does this Tunisian guy have special qualifications that a british won't have!

No. Should they separate or Divorce his Visa becomes invalid and you as an Employer would be liable to a fine of up to £10,000 for employing an `illegal` worker.