Brits: what does the term "tactical voting" mean?

You’ve got this backwards. Philip Hammond stood down and did not contest his seat.

Dominic Grieve did contest his seat as an Independent. He came second.

Oops, quite right. Thanks for the correction.

UltraVires

Aspidistra gave the numbers for the Australian Liberal Party as 80k = 0.5% of registered voters. The Australian Labor Party are about 50k members though the majority of trade unions in Australia are affiliated to the party at a state level.

At the preselection meetings (for all the major parties at least ***) all votes counted have equal weight and you need to be present to vote.

No, it doesn’t shut out the moderates. The party branch membership may well be more ideologically true but getting their man or gal into parliament is the aim of the game and in Australia the parliamentary members are almost without exception centre left to centre right. (because of compulsory voting and the bulk of the electorate are centre/moderate). A key determinant of a candidates ideological alignment is which political party faction the candidate comes from or joins.

The rather small number of hard or radical Left/Right nutters who get into Parliament either do so via the Senate (Leyonhjelm, Anning, Carr, Cameron, Bernardi, Hanson-Young etc.) by virtue of proportional voting from party lists or standing as independents. Independents only win if they get the votes from at least one of the majors so most independents are populist rather than radical.

For the ALP the principal policy forum is the National Conference, held every three years. This forum determines the ALP parliamentary party policy. For the Liberal Party the equivalent is the Liberal Federal Council which meets annually and advises but doesn’t set policy for the Parliamentary party.
There are multiple ways to become a delegate to either of the party’s national forums but you need to be more than a rank and file party member

*** I don’t know well how Pauline Hanson’s One Nations or the Palmer United or Bob Katter’s Australian Party or Fred Nile’s Christian Democratic Party function but suspect the membership are rather more acquiescence of the party talisman’s wishes.

Not in Canada. As one Liberal political operative is reported to have said in last year’s SNC-Lavalin matter, “It doesn’t matter how good our policies are if we can’t get elected to implement them.”

The Liberal Party of Canada is one of the most successful political parties in western liberal democracies. It held office for 70 years during the 20th century. Normally that sounds like a corrupt electoral system, but Canada’s elections have been free and fair for all that period.

Rather, the Liberals have been the ultimate centrists. They’ve been described as the black cat of Canadian politics, with nine or more lives, and always prowling around the centre. Going left when they sense the electorate is going left, shifting right if the electorate is shifting right, but always near the centre.

Interesting article in the New Republic from four years ago, when Trudeau defeated the Conservatives and won a majority: Why Is Canada’s Liberal Party So Dominant?. (Note that the article points out that Duverger’s [so-called] Law has never applied to Canadian federal politics, a point I keep making whenever FPTP comes up as an explanation for the inevitability of the US two-party system.)

The Political Parties, Elections and Referendums Act 2000 and the Registration of Political Parties Act 1998 sharply reduced the ability of people to form political parties and to describe themselves on the ballot. Partly this was because the various forms of party list-based proportional representation to used for the Scottish, Welsh & Northern Ireland devolved assemblies required a much sharper control over straw-man parties. Also the ‘real’ politicians were getting tired of people calling themselves silly names or deliberately confusing ones.
Previously, if you wanted to run as ‘Real Conservative Candidate’ there was nothing to stop you. In the 1982 Glasgow Hillhead by-election one of the candidates changed his name to Roy Harold Jenkins and called his party affiliation Social Democratic Party, hoping to cause confusion with the much better known Roy Jenkins, who had been a Labour politician and had changed to form the SDP with the so-called ‘Gang of Four’ The late Cmdr. W.G. Boakes used to run as ‘Public Safety Democratic Monarchist White Resident’, and consistently came last - probably because he refused to do any campaigning, maintaining that the name told the voters all they needed to know.
Now your party had to be registered with the Electoral Commission, who could rule on what you could call it. If they didn’t like what you wanted they would refuse to register it, and you would just have to run as ‘Independent’ (many people do).