Properly spelt "bar t'at" I suppose. The English preposition "bar" is fairly old but still in common usage. T'at for "the hat" is not particularly common South of Doncaster.
"Bar" meaning "all excepting" as in racing odds for all horses on 'long' odds. Horse 1 @ 6 to 5 on, horse 2 @ 2 to 1, horse 3 @ 3 to 1, horse 4 @ 6 to 1. "20 to 1 Bar" ( i.e.the horses not previously given specific odds are all at 20;1)