LyrArc Article Gist
An obscure parliamentary precedent was used by Speaker Bercrow to end Theresa May's strategy of repeated votes in Britain's parliament to browbeat reluctant Brexiters to vote for her negotiated settlement with the European Union. The precedent was set as far back as 1604 and was designed to protect the powers of parliament in the face of a Scottish royal assuming the role of sovereign of Britain. Repeated votes on the same proposals are not allowed if the intention is to find ways to get reluctant members of parliament to vote in favor, essentially by bullying them into this. This is also why Brexiter MP's have hailed the Speaker's decision in their opposition to Theresa May.

Britain's constitution is based not on a single document like the U.S. Constitution. It is based on a a collective set of laws and precedents. A parliamentary rule book published by Thomas Erskine in 1844 sets out these rules in 1097 pages, available for 439 pounds in parliament's bookshop. It has gone through 24 editions. Speaker Bercrow says of the rule he was referring to as a statement on page 397 of the 24th edition. 

There is not much time, just 10 days, for prime minister Theresa May to end the current parliamentary session and call a new one to nullify Speaker Bercrow's decision. This would also further antagonize the 40 Brexiter MP's led by Mr. Jacob Rees-Mogg and Boris Johnson in May's own party, making it impossible for parliament to agree on a course of action.