Can the Prime Minister prorogue Parliament?

Question

Can the Prime Minister of the UK prorogue (ie. suspend) Parliament at any time?

Or are there constraints on this?

Answer 1

Short answer: yes, the PM can prorogue Parliament at any time.

Long answer:

In theory, it's the Queen who prorogues Parliament:

The Queen formally prorogues Parliament on the advice of the Privy Council.

However, like so much of the British constitution, theory and practice are not quite the same thing. The practice is that the government decides when the current session should end, and when the next one should begin.

In more normal times, this tends not to be a controversial matter, so whether the decision is taken by the PM, or by those responsible for the parliamentary timetable (e.g. the Leader of the House), is not normally important.

As I commented in an answer to a related question:

By convention, sessions normally last one year; and before the passing of the FTPA [Fixed Terms Parliaments Act], they typically ran from November to November. In those years where there was an election (normally in May), there would be a short session before the election (Nov - May), and a longer one after (May/June to Nov the following year).

However, since the passing of the FTPA, sessions have run from May one year to May the next year, to fit with the new election cycle; hence the session after the 2015 election was one year. However, the snap 2017 election took place in June that year, and so the session which followed was expected to run from then until May 2019.

Beyond this, British governments have mostly stuck to convention when it comes to prorogation. The last time this power was used for tactical reasons was in 1948, when a 10-day session was held as part of the process of passing the Parliament Act 1949.

By comparison, in Canada (which otherwise follows similar practices to the UK in this matter), the federal government has used the prorogation power much more recently for political reasons, as has one provincial government.

As of May 2019, the current session is still running, and there's been no word of it ending. This is highly unusual for the UK. Ultimately, the government will decide when the session should end, and because of the unusual circumstances, one can imagine that the PM will have the final say.

Regarding constraints: from a practical point of view, Parliament cannot be prorogued for too long (i.e. the gap between sessions cannot be too long), as parliamentary authorisation is needed at least annually to fund the government, levy some taxes, and maintain the armed forces.

Besides that, the FPTA means that the next election will be held in May 2022 unless Parliament determines otherwise - but such a change is only possible if it's in session!