Are there influential theories why the Lib Dems have survived on the UK political landscape?

Question

Generally a first-past the post FPTP electoral system favors a two-party system, aka Duverger's law.

In the UK however, the Lib Dems have managed to survive for (approximately) a century the appearance of Labour, albeit with a substantially reduced electoral/seat share.

Are there any influential theories in political science why the Lib Dems were not eliminated (rendered entirely obsolete) in UK politics?

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This is not a duplicate of the UK vs US question. The accepted answer there doesn't even mention the libdems; it talks about the SNP, which is a regional party, and a recent one to boot. Basically that answer is completely sweeping under the rug the libdem issue. Also that question is frankly rather broad; maybe someone will chose to say something about libdems there, maybe not. Actually one answer (the 3rd one by votes right now) does mention the libdems:

The Liberal Democrats have taken their traditional pro-EU center-left position, but now their campaigning is emphasising their EU policy rather than their center-left.

That hardly explains why they survived for 100 years contra to Duverger's law.

Answer 1

The UK has quite small constituencies, This allows for a third party that is polling at 15% nationally to achieve a plurality in a few constituencies.

In the period after the rise of the Labour Party in the 1920s, the Liberal party engaged with and was part of various "National" governments. In areas where there was little support for Labour, the Liberals remained the natural local opposition to the Conservatives, and in areas where there was very little Conservative support the Liberals became the natural opposition to Labour. Using "localism" allowed the Liberals to continue until after the war.

In the years following the war, the Liberal party did become very weak, and only a few locally popular MPs remained. However in the late 60s and 1970s the power it wielded due to the governments having very narrow majorities caused it to remain relevant.

The split in the Labour party in the 1980s caused a major increase in support. The SDP entered a formal alliance with the Liberals. This gave them many more MPs. Outside of General elections, they were the natural target of protest votes against the main parties. As local council elections often happen during the Mid-term, they built a strong network of local councils and councillors.

A party that can hold onto a good number of councils and can poll at 15% can continue to win seats in Parliament, especially when there are 650 seats and so a few popular local candidates can get a plurality locally.

So the continued survival of the Liberals is due to: Small UK constituencies, A focus on localism, Targeting a few winnable seats, Being willing to deal with other parties, Having a strong base in town and county councils.