I have an existing flue approx 9 inches in diameter which was used for my gas fire. I am going to have an open fire and have been advised that the flue is okay to use as it meets the 200/225mm regs. I am unsure if the flue is high enough to accommodate a coal/log fire. It is located on the edge of the house at the side and looks as if it is approx 3 feet above the roof tiles. It doesn't rise above the tallest part of the roof which is some way away due to the flue being located on the outside wall of the house.

Does the flue need replacing with a taller one or can this accommodate a coal fire?
It has a cowl over already and has been working fine with a living flame gas fire for many years.

Chimney terminations need to be 2' taller than any roof within 10'. Unless your roof is nearly flat you are not meeting this rule. Where do you live?

I live in Dorset. Would the requirements for the gas fire use have been different to that needed for a coal fire?

gas fire use have been different to that needed for a coal fire?
Yes, you should consult a knowledgeable technician. Clearances for a gas log fireplace with a flue and a coal or wood fireplace with a chimney are quite different.

I am not familiar with the regs in the UK. What is the "it meets the 200/225mm regs"

Also are you sure the flue is OK for a real fire ( not a gas fire) most flue for gas burning do not meet the safety requirements for wood fires. So have you had the flue actually inspected by someone?