This sounds like a wonderful idea, but how exactly would it work? Suppose that a busload of MPs goes over a cliff. We have 78 by-elections, and 78 new MPs. A basic principle of our Constitution, if not of logic itself, is that no one can dictate to these MPs how they will vote when they get to Parliament. Income tax is an annual tax for which the authority to raise it has to be renewed every year. It is not possible to dictate to any of these new MPs, or to any existing MP for that matter, how they will vote. In the case of other taxes, such as VAT, Parliament could resolve to determine the VAT rate at the start of a new Parliament, and not to review it, but there can still be a palace revolution after which the new regime changes it.
There are historical precedents here. We had a palace revolution in 1940 when Winston Churchill took over as Prime Minister even though Neville Chamberlain stayed on as leader of the Conservative Party for a few more months. The Labour Government of the late 1970s lost its majority thanks to by-elections. It is hard to see what a law against tax rises would actually involve.
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