A blundering bodyguard of former British Prime Minister Tony Blair left a loaded pistol inside a Starbucks bathroom during a pit stop while on duty.

The semi-automatic Glock 17 remained on the floor of the coffee shop’s only toilet for nearly 20 minutes as Blair's close protection officer tried to retrace her steps.

It was eventually found by a horrified Starbucks employee, who called police.

The gun was linked to the officer when cops compared its serial number to those logged at a police armory. She was “removed from operational duties.”

“She knows she has messed up bad,” a senior police source said Wednesday night

After leaving the bathroom, the officer stopped to buy a coffee and then walked out — completely forgetting she had left the gun behind.

“Luckily it was found in time, but if a child or a criminal had picked it up there could have been terrible consequences," the police source said.

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