I'm now starting to come around to the idea of this, as it's a practical certain vote loser for the tories, not that we needed many more considering their latest approval ratings.
Anyone under 50 should absolutely hate the imperial "system", and would be another good reason to ditch the tories, if they were leant a vote. Anyone imperial/ old/ old fashioned is probably already voting tory anyway, no matter what.
Also, in real life it won't make a blind bit of difference, as cars are still mph, pints are still pints, golf is yards, so is football, and engineering and construction will never move away from metric, currency will remain as it is etc.