The two-Michelin starred chef's restaurant at the property, run by head chef Mark Rossi, was ranked below the city's Age Concern day centre, which received a full five-star rating by hygiene inspectors, reports the Daily Telegraph.
The one-star rating means "a poor level of compliance with food safety legislation - much more effort required".
Declan Kelly, the hotel's general manager, explained that the restaurant was in the process of changing health and safety consultants at the time of the inspection in February.
"I am afraid procedures were not adhered to as strictly as we would have liked and we did not perform as well as we should have," he told the Telegraph.
"The issues have been addressed and I am very happy with the systems we now have in place. I just wish we could be re-assessed because I am very confident we would score very well.
Caines heads up the kitchen at two-Michelin starred Gidleigh Park in Devon as well as overseeing signature restaurants at four Abode Hotels. He relaunched the restaurant at the Bath Priory in March, taking his eponymous restaurant total to six.
In an interview with Caterer earlier this year, Caines revealed plans to bring his restaurant empire to 10 by 2012.
By Daniel Thomas
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