With the fate of Brexit in the balance and an embattled prime minister in trouble, a decision by British MP to debate the height of letter boxes raised more than a few eyebrows.

The 10-minute rule motion, a procedure allowing MPs to state their case for a new bill, was held just after Prime Minister Theresa May faced angry questions in parliament.

"Having delivered newspapers as a boy, I fully understand the challenge of low-level letterboxes. However, I feel that our government have slightly more important things to discuss this afternoon," @TweetingBeattie wrote on Twitter.

"Gotta smile at our democracy sometimes," said @AidanMelville, while @acoulton wrote: "Crazy times".

But Liberal Democrat lawmaker Richard Newby said he was "pleased" parliament was "getting its priorities right".

"Anyone who's ever been leafleting knows how irritating low-level letterboxes can be," he wrote.

In parliament, Conservative MP Vicky Ford, who brought the motion, said her proposed legislation to amend building regulations had "a huge amount of support".

Ford said her initiative was a health and safety issue because post workers often faced "repetitive stress" and "back pain" from having to bend over to post letters.

"Let us now deliver for them," Ford said.

The MP also pointed out the existence of a European standard for a minimum height of 70 centimetres for letter boxes.

"Not all European standards are evil. On this special day, wouldn't it be nice to find one -- at least one -- we can all unite on," she said.