Speaker Bercow has just ruled that there can’t be a third vote on Theresa May’s Brexit deal unless it is substantially altered.
While I’ve questioned Bercow’s handling of Brexit in the past, this ruling is spot on. Erskine May, the ‘bible’ of parliamentary procedure, is quite clear on that point: “A motion or an amendment may not be brought forward which is the same, in substance, as a question which has been decided in the affirmative or negative during the current session.”
This rule is an old one. It first appears in the Journal of the House of Commons in 1604, and two years later, a bill was kicked into the long grass because it dealt with matters that had already been discussed earlier in the session. Since then, successive Speakers have upheld the rule on numerous occasions.
It may seem odd that Bercow is suddenly relying on precedent given his willingness to bend the rules in the past. But while parliamentary procedure needs to change with the times to avoid becoming fossilized, that doesn’t mean every precedent should be jettisoned. The Government should not be allowed to wage a war of attrition by forcing MPs to vote on the same issue again and again, so in this case, it makes sense to enforce the precedent.
The Government is not completely helpless in the face of Bercow’s ruling, either. Ministers ultimately control the timing of a parliamentary session through the royal prerogative power of prorogation. If the Queen were to prorogue Parliament, it would usher in a new session and the Government could legitimately ask MPs to vote on the Brexit deal again. However, this would have a major downside: any bills that are currently before Parliament would lapse at prorogation, meaning they would have to start again from square one in the new session. Carry-over motions could alleviate some of the pain, but it wouldn’t be a perfect fix.
UPDATE: since posting this, it has occurred to me that the Government has another way forward. Ultimately, MPs decide how to conduct their business, so ministers could theoretically table a resolution declaring that, notwithstanding the House’s usual practice, MPs can have another vote on the Brexit deal. Whether the House would agree to such a resolution is anybody’s guess, though.
 Sir Barnett Cocks, ed., Erskine May’s Treatise on the Laws, Privileges, Proceedings and Usage of Parliament, 18th edition, (London: Butterworth & Co. Ltd., 1971), 362.
 “House of Commons Journal Volume 1: 02 April 1604,” in Journal of the House of Commons: Volume 1, 1547-1629, (London: His Majesty’s Stationery Office, 1802), 161-162. British History Online, accessed March 18, 2019, http://www.british-history.ac.uk/commons-jrnl/vol1/pp161-162.
 “House of Commons Journal Volume 1: 08 May 1606,” in Journal of the House of Commons: Volume 1, 1547-1629, (London: His Majesty’s Stationery Office, 1802), 306-307. British History Online, accessed March 18, 2019, http://www.british-history.ac.uk/commons-jrnl/vol1/pp306-307.
 For a partial list, see Erskine May, 362, note (f).