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MartinII So long as to don't do around flying it upside donw, no one will know. ;) It doesn't make sense, however, for those who claim to be so proud to be British that they feel compelled to tie the Union Flag to lamposts, to not know which way up it's meant to be. It's quite obvious that one or more are upside when there is more than one flag and they're not all the same way up.
Just so you can spot them yourself, the broad white stripe is uppermost on the side next to the hoist. If there is no hoist, it's deemed to be on the left.