OK, the British Union Jack is shown flown on the stern of the Red Funnel. IRL, the Union Jack is flown only at the bow of British warships when moored or anchored. I believe that certain other vessels (Fleet Reserve, yacht clubs) may fly it also, but always up front, at the stem of the vessel. The Brits have three nautical ensigns of which I am aware. The English "Cross of St,. George" with the Union Jack imposed in the upper left corner is flown by Royal Naval Vessels. The lesser known blue ensign with the Union Jack occupying the upper left quarter is flown by Fleet Reserve (civilian manned RN support vessels) and Royal Mail ships, such as the RMS Titanic. I think that this flag may be flown on UK registered ships on which the master is a retired RN officer. The "Red Duster," red with the Union Jack imposed in the upper left quarter is flown by the rest of UK registered vessels. In fact, the "Red Duster" is flown as a courtesy flag by foreign ships when in UK waters. I know of absolutely no cases in which the Union Jack is flown from the stern of any UK registered vessel. If I am incorrect, I would greatly appreciate any clarification. Thanks.
Fred
See:
http://en.wikipedia.org/wiki/List_of_British_flags