The Merchant Navy were indeed a fundamental part of the war effort for the besieged United Kingdom and many merchantmen were armed to assist in protecting convoys. A good number of these otherwise 'civilian' vessels also carried men from the Royal Navy to man the guns.
The Merchant Navy is remembered on a large number of special war memorials in our port cities, such as Liverpool, Bristol, London, Southampton etc and they play an active role in the Rembrance Day services in London and elsewhere with the Naval and Military forces each year.
If you go to http://www.nationalarchives.gov.uk/records/merchant-seamen-medals-ww2.htm you will find that the UK Government awarded no fewer than nine different medals to merchant mariners.
The War Medal 1939-1945;
Atlantic Star !939-1945
1939-1945 Star
Africa Star 1940-1943
Pacific Star 1941-1945
Burma Star 1941-1945
France and Germany Star 1943-1945
Italy Star 1943-1945
Obviously it depended on the routes that their vessel plied and the dates in which they served in specific areas which were regarded as theatres of war for the time-being.
My uncle was on fast motor boats on the Atlantic approaches and the coastal waters around the UK and Ireland on the Atlantic coastline,. His boat was one of many active on anti-submarine activity to try and protect the Merchantmen on the final legs of their perilous journey from the USA and Canada. He was awarded the Atlantic Star.
Personally I think that the the civilian sailors of the merchant fleet richly deserve inclusion as war heroes!
Regards
John