The whole beauty of the British (Imperial) system,Jake, and the reason why it was such a success for centuries, is that the various units were fashioned to suit the needs of the people.
The person-in the street was happy with inches, feet and yards, but the surveyor liked chains, the racing man furlongs and hands, the engineer thous, the sailor cables, and so on. And the same with weights and other measures. The system conformed to Man.
The metric system, on the other hand, had nothing to do with human beings: an arbitrary fraction of the earth's circumference was chosen as a unit and then multiplied up, or divided down, by ten. And that was it. If it didn't suit..tough. Man had to conform to The System. ("Vee haff vays..."). Bland, authoritarian and insulting � with its implication that we�re all too stupid to be able to multiply and divide by anything but ten.
As for road signs, I don't think you�ve thought it out (and surely the Irish system of mixed signs must be a joke?).
Think of all those large blue motorway signs, all of which will have to be taken down, not only for altering but for repositioning. And the overhead gantries. For how long are large sections of our motorways going to be out of action? Then you have the slip-roads, roundabouts, dual-carriageways, A-roads, B-roads, country lanes, village streets, little finger-posts. The government's estimate of �700 million, like all such, is way too low, more sensible predictions being between �1000 million and �2000 million.
What Chancellor is ever going to stand up on Budget Day and say that the thousands of millions that he was going to put into hospitals and schools is going to be used instead to change our milk bottles, beer glasses and road signs? There�d be civil war. You�re lumbered with a mixed system now � all the fault of the metricists.