I am having problems with a company who are stating that for hot works they can have a fire extinguisher withing a 200m2 location of the work being carried out

It is you who should issue a hot work permit and include a statement stating "At least two suitable extinguishers or a hose reel are immediately available. Both the personnel undertaking the work and providing the fire watch are trained in their use." and  within a 200m2 is not acceptable, it's you who have control.

Check out http://safecontractor.com/getattachment/Services/Contractors/Guidance-notes/Hot-Work-Permit-Guidance-Note-SA-GN-19-(V1)-Jan-2014.pdf

They are mixing up the general floor calculations in BS5306-8 for general normal risk cover by Class A extinguishers. Hot works are by their nature anything but normal risk and require extinguishers immediately available (certainly within 10m).

No extinguishers no permit, no permit no work, leave the premises, don't expect to be paid for your time.

Many buildings that are normally very safe suffer devastating fires during hot works - the risk is too great to let them get away with this misguided statement.

If they can't be bothered to spend the very small amounts on having & maintaining a stock of extinguishers for hot works I'd be suspicious of what other corners they will cut in both safety and workmanship.