LONDON (Reuters) - Seven Roman Catholic priests were refused service in a Welsh pub after staff mistook them for a stag party in fancy dress.

After realizing a mistake had been made, Cardiff's City Arms offered the clergymen a round of free drinks to apologize, the Archdiocese of Cardiff said in a blog post on Tuesday.

Arriving at the pub on Saturday to celebrate the ordination of Father Peter McLaren, the priests were told by a bartender that the City Arms did not serve large groups in fancy dress.

The archdiocese said they had started to leave when another staff member said he believed they were real priests and invited them back in for a free drink.

"We'd like to thank The City Arms for being good sports through all of this and their kind gesture to our seminarians," the blog post said.

It said the priests had initially thought the bartender was joking when he mistook them for a stag party, an all-male bash held for men who are getting married and which in Britain often involves dressing up and consuming copious amounts of alcohol.

An assistant manager of the pub told the BBC that it was the policy of the pub to turn away large parties wearing fancy dress as there had been a number of issues with such revelers.

"A slight misunderstanding from us but everyone was happy in the end," the pub said on Twitter.

(Reporting by Alistair Smout; Editing by Catherine Evans)