Parliamentary procedures and conventions are often dismissed as ‘arcane’ or ‘byzantine’ by commentators. Still, on occasion, they can have a significant impact on politics – as demonstrated by the recent furore over a Labour amendment to the Gaza ceasefire motion in February.

Last week, a new paper in the House of Lords was published which has the potential to have a similar political impact – and could even save the government’s controversial Rwanda Bill, which is in its Report Stage today.

The paper, by the convenor of the crossbench peers Lord Kinnoull, is on the Salisbury-Addison convention, which says that the Lords will not vote against Bills which were in the government’s manifesto. The convention began in 1945 to deal with the relationship between a Labour government and a House of Lords filled with hereditary Conservatives.

The idea underpinning the convention is that manifesto bills enjoy a special form of democratic legitimacy as, directly or indirectly, they have been endorsed by the electorate.

In its current form the convention has evolved to mean that the House of Lords will give a manifesto Bill a second reading; it will not be subject to ‘wrecking amendments’; and it should be returned to the Commons in reasonable time. These protections are important when a government wishes to pass contentious legislation, especially ahead of a general election.

At present, the Rwanda Bill does not seem to benefit from these protections in the Lords. The 2019 Tory manifesto promised to ‘establish immigration controls’ but was mainly concerned with a points-based immigration system. There was no mention of the Rwanda plan.

Lord Kinnoull’s paper though examines the meaning of a ‘manifesto Bill’ and reaches a potentially surprising conclusion.

One of its more striking suggestions is that even if a Bill wasn’t explicitly set out in a manifesto, it may still be protected by the convention. The paper also suggests that there may be other elements that the Lords should consider when determining if a Bill should be protected, including whether the policy area featured in the most recent King’s Speech and whether the Bill has been passed by the House of Commons.