Manroy Engineering Ltd. has been a supplier of spares to the British Army since 1975, following the Falklands War.  They make updated versions of the venerable Browning .50 caliber machine gun, the standard Nato 7.62 machine gun, 20 mm guns and all the associated  mounts and turrets.  They can adapt any of their guns to any kind of vehicle, whether land, air or sea based.  Their M2 heavy machine gun features a quick change barrel assembly, reducing the danger of messing up the headspacing when installing a new barrel.  A standard M2 barrel can still be used in an emergency, but must be headspaced in the old manner. 

Manroy is the last producer of heavy machine guns in the UK, and  recently raised 6 million euros by trading on AIM, London's stock market for smaller companies, according to a story in the Telegraph. One builder of heavy machine guns for a country like the UK doesn't seem like enough.

Prince Harry with Manroy M2

Prince Harry using a Manroy M2 in Helmand Province, from the Telegraph