I cannot understand all the huffing and puffing from senior Labour figures and some constitutional pundits about the proposal that the five year fixed term of future parliaments should not be curtailed unless 55%, rather than a simple majority of MPs, vote for it. It seems reasonable to assume that a major change, such as the highly desirable move to a fixed term for parliaments, should involve other consequential adjustments. If the prime minister is no longer able to bully his critics into line by the threat of a dissolution (or, strictly speaking, asking the monarch for a dissolution) than smaller parties, or even individual MPs, should not be able to blackmail an administration by a similar threat.
I believe that in Scotland, which also has fixed term parliaments, the barrier is set at 66%. Compared with this 55% seems modest. The rule would not mean that a government defeated by only one vote would necessarily remain in office. Theoretically the government so defeated would resign and the monarch would invite another leader, or maybe even the same leader, to try to form an administration with a different composition which could command the support of the existing parliament. It would be interesting to see these circumstances tested in practice before such rules are codified in a written constitution (which doesn't, at the moment, appear to be on the agenda)
In the event of deadlock, without a written constitution with safeguards requiring a higher majority for constitutional changes, there would be nothing to stop a parliament overturning the 55% rule by a simple majority, and then the prime minister asking for a premature dissolution.