Do the maths: Why Lib Dem threats might not add up

As the Lib Dems threaten to take down the government's plan to introduce a right to buy for housing association tenants, tearing up the House of Lords' hallowed "Salisbury Convention" in the process, it's worth remembering one key point; they can't do it alone.

Do the maths.

In the Lords, the Government has just under 30% of peers, with Labour about the same.

The Libs have 13% and the Crossbenchers just under a quarter. So a government defeat will pretty much always require Labour peers to turn out. (You can spin a scenario involving a massive Tory rebellion topped up by Crossbenchers and Libs, which could succeed without Labour, but it's hard to imagine what issue would produce such an alignment. Labour are the necessary keystone of any government defeat in the upper House.)

This ever-helpful site provided by UCL's Constitution Unit anatomises each government defeat - and rather underlines the point.

There is no doubt that the Lib Dems are hungering for revenge on the Tories for their election drubbing, and that their solid disciplined phalanx of peers is one of their few remaining political assets. But the snag is that it only really delivers in co-operation with others.

There are other conditions that have to be met as well. Turnout matters a lot on these occasions. It is sometimes easier for government peers to discover an unavoidable social obligation than to actually vote against their party, and, in any event, there's always a better chance of mustering an anti-government majority before the 7.30pm dinner break, rather than after it.

And one interesting question, which has yet to be answered, is the extent to which Labour peers will be ready to turn out in the cause of the Corbyn Labour party - and that may depend on whether the precise point at issue in a particular vote sets hearts a-pounding.

And what of that Salisbury Convention? Labour have pointedly said they will operate within the conventions of the House of Lords, and that includes Salisbury-Addison.

This was the deal reached between "Bobbety" Salisbury, Lord Cranborne, (later the fifth Marquess of Salisbury), the Tory leader in the Lords, and his Labour opposite number, Lord Addison, in the wake of Labour's 1945 electoral triumph.

(Confusingly there's a Salisbury doctrine dating back to the 1880s Victorian PM - the third marquess - which assumes the Commons does not always represent the people and that the Lords can therefore claim a right to refer contentious legislation back to the voters, by rejecting it - but when people talk about the Salisbury Convention now, they usually mean the 1945 one.)

No opposition

Clem Attlee's Labour government had a massive Commons majority and an undoubted mandate, but had only 16 peers in the Lords. Theoretically, their Lordships could have frustrated Attlee at every turn, throwing out or wrecking every bill in their programme, but that would have risked retaliation in the form of outright abolition - so, instead, a deal was struck.

Peers would not oppose measures promised - "foreshadowed" - in the government's manifesto, and therefore assumed to have the endorsement of the electorate, at second or third Reading. In other words, the government would get the legislation it had promised to voters, and therefore would not have to get bogged down in an Asquith-style struggle with the Lords - Addison was a veteran of the Asquithian Liberal Party, and would doubtless have preferred not to repeat its epic battles with peers.

Cranborne spelled the new doctrine out in the debate on the King's Speech in July 1945:

"Whatever our personal views, we should frankly recognise that these proposals were put before the country at the recent general election and the people of this country, with full knowledge of these proposals, returned the Labour Party to power. The government may, therefore, I think, fairly claim that they have a mandate to introduce these proposals. I believe it would be constitutionally wrong, when the country has so recently expressed its view, for this House to oppose proposals which have been definitely put before the electorate."

He reserved "full liberty of action" on legislation not included in an election manifesto.

Thus it was possible in 2000 for peers to throw out, at second reading, the Criminal Justice (Mode of Trial) (No. 2) Bill, which would have curtailed the right to trial by jury, but which was not a manifesto bill.

And more recently, in 2011, it was possible for Labour's Lord Rea to ask peers to throw out the Health and Social Care Bill at second reading, on the argument that the Conservative election manifesto had ruled out "top-down" reorganisations of the NHS, when the bill amounted to exactly that. (In fact the whole Coalition period raised questions about how the Salisbury convention could apply, when no one party had won the election. Could the post-election Coalition Agreement - not sanctified by the electorate - assume the role of the manifesto of a winning party?)

There's also a teasing issue about what, exactly, is promised in a manifesto. The promises are often vague and easily manipulated and governments have frequently jettisoned inconvenient ones - so there's an argument that if ministers are not to be held to their own promises, maybe Parliament should not have to be over-respectful of them.

In any event, the 1945 convention left open the possibility of peers making merry during detailed debate at committee and report stage consideration, with amendments which could substantially change the legislation in question - with debatable territory in the middle where peers could argue about whether an amendment was "helpful" and simply improving the government's proposal, or "wrecking" and designed to frustrate the manifesto promise to voters.

More than half a century on, the Lib Dems were arguing that the Constitution has changed since 1945. Lord McNally, then leader of the Lib Dem peers noted in one Lords debate (they talk about this rather a lot…) that "to resurrect a 60-year-old convention that was offered by a Conservative-dominated hereditary House to a Labour government with 48% of the vote, and then to say that that should still apply to a Labour Party that is now the largest party in this House, but is a government with 36% of the vote, is stretching the limits of the convention."

And they suggested a number of get-outs from it - public opinion, the solidity of support for the government on its own backbenches, the time since the general election at which a manifesto was presented, and a special responsibility for the Upper House to protect the Constitution and civil liberties.

But they may not need to break the Salisbury Convention to make the sell-off of housing association properties much more difficult, with some clever amendments about safeguards or local checks and balances.

So where does that leave us?

The Lib Dems seem to hope they can drag Labour along with them, in defiance of the conventions, to vote down more government legislation. We don't yet know whether a Corbyn leadership might be inclined to do so, and we don't know if individual Labour peers would come out to play, even if they did.

The conventions of the Lords are powerful things, and impose deep inhibitions on many peers. The Lib Dem peers might just be able to put themselves at the centre of resistance to government legislation, but what if they give an insurrection and nobody comes? They could end up flailing around, if Labour don't join in.

As the Lib Dems threaten to take down the government's plan to introduce a right to buy for housing association tenants, tearing up the House of Lords' hallowed "Salisbury Convention" in the process, it's worth remembering one key point: they can't do it alone.