The pair aged 50 and 43 swore in front of children, refused to return to their seats and tried to force their way into the cockpit after being seen drinking Malibu from the bottle on a Tunisia-bound flight, the Daily Mail reported.
The two women allegedly hid in the Boeing 737-400's toilet at 30,000 ft for a smoke.
"Monday's BA2664 service from Gatwick to Tunis was diverted to Lyon following the continued disruptive behaviour of two female passengers," a British Airways spokesman said.
The pilot diverted the airliner to Lyon, where French police boarded and arrested the drunk women.
"Our customers and flying crew deserve a safe and enjoyable flight experience. We do not tolerate any disruptive behaviour on board our flights," spokesman added.
The duo even allegedly threatened to track down and kill the family of the stewardess on board.
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The two women may face a lifetime ban from British Airways.
"They decided they were going to meet the captain and marched towards the cockpit. It was very frightening," a passenger was quoted as saying by The Sun.