Do we need a written constitution in Britain? The question is not a new one – I seem to have been writing essays on it since my schooldays – but it has now been raised by no less a body than the political and constitutional reform committee of the House of Commons.

Looking ahead to the forthcoming 800th anniversary of an earlier constitutional document, the MPs ask whether it is time to start writing a new Magna Carta.

For now, they have studiously avoided answering that question, though the committee would not have commissioned a four-year research project leading to a 420-page report if all its members were happy to leave things as they are. Reminding us that the UK, Israel and New Zealand are the only democracies in the world that have not codified their constitutions, the MPs are seeking public responses by 31 December, so that they can make recommendations before the general election.

All but a few pages of the committee’s report were written by Robert Blackburn, a solicitor and professor of constitutional law at King’s College London. He begins by setting out 21 arguments in favour of codification. ‘A written constitution would circumscribe the boundaries of the British state and its relationship with Europe and the world,’ he writes. ‘It would become a symbol and expression of national identity today and a source of national pride.’

Putting it simply, it would tell us how we are governed.

There is a lot to be said for a constitution that would limit the powers of our ‘elective dictatorship’.

On 10 July, the day the government announced that its Data Retention and Investigatory Powers Act would go through both houses of parliament within a week, Lord Woolf initiated a debate in the House of Lords on the rule of law. The former lord chief justice recalled that Tony Blair’s government had changed ‘overnight’ the status of a historic constitutional bulwark. No longer the judges’ representative in cabinet, the lord chancellor is now merely ‘qualified by experience’.

But, referring to Chris Grayling, Woolf was not at all sure what form that experience took. ‘Unlike the old-style lord chancellor, [Grayling] sees his current role as being only one more step in what will no doubt be a glittering political career,’ the former chief justice said.

And that career now glitters ever more brightly. Grayling survived last week’s ministerial cull and no longer finds himself fighting the attorney general over human rights: Dominic Grieve has been replaced by Jeremy Wright, a former minister in Grayling’s own department.

But there is a lot to be said against a written constitution. ‘It is unnecessary, undesirable and unBritish’, says Blackburn, summarising his 21 counter-arguments. An unwritten constitution is ‘evolutionary and flexible in nature, more easily enabling practical problems to be resolved as they arise… than would be the case under an entrenched constitutional document’.

Codification would politicise the judiciary, Blackburn continues, requiring courts to decide questions that are best left to politicians. There is apparently little public support for something that would need a huge amount of legislative time to implement — not least because the politicians would never agree on what it should say.

Blackburn then goes on to offer us three illustrative blueprints. The first, which he describes as a constitutional code, would be no more than a handbook, with no statutory authority. The second, consolidating legislation, would bring together existing statutes and codify constitutional conventions.

Only the third would be a true constitutional document, governing the way the country is run. Each blueprint is self-contained but Blackburn regards them as stages on the road to full codification.

Blackburn’s first blueprint – his constitutional code – is a masterly summary, in fewer than 100 short paragraphs, of the constitution as it now stands. His second blueprint, the consolidation and codification statute, is rather less satisfactory, including language that is archaic, aspirational or merely imprecise. Even though Blackburn attempts to make his constitutional conventions non-justiciable, some aspects of government are best left fluid. But his draft bill is still an impressive summary of our present constitution in 231 clauses.

Then we reach the real substance of the paper, Blackburn’s 53-clause codified constitution. Though he insists that it is merely illustrative, his draft would make major changes, redefining British nationality; creating a director of civil proceedings with power to control constitutional litigation; and replacing the House of Lords with an elected second chamber. Crucially, the courts could make declarations of unconstitutionality and, in unspecified circumstances, declare laws invalid.

These are deep waters. Do we really want such a fundamental shift of power from parliament to the judges? Do ministers? Or MPs? I very much doubt it. And, unless we think a future government might think otherwise, codifying the constitution is either unattainable or pointless.