Poland, the pivotal power in post-communist central Europe, is in danger of being reduced by its recently elected ruling party to an illiberal democracy. Basic pillars of its still youthful liberal democracy, such as the constitutional court, public service broadcasters and a professional civil service, are suddenly under threat. The voices of all allied democracies, in Europe and across the Atlantic, must be raised to express their concern about a turn with grave implications for the whole democratic west.

And this needs to happen soon. For the political blitzkrieg of the past two months suggests that the strategy of the Law and Justice party (known by its Polish acronym as PiS), and specifically of its one true leader, Jarosław Kaczyński, is to do the dirty work of transforming the political system rapidly, even brutally, and then to show a kinder, softer, more pragmatic face. He has the parliamentary majority to do this (although not the two thirds needed to change the constitution), still considerable popular support – and, shockingly, the president of the country is behaving like his glove puppet.

For at least 20 years Kaczyński has dreamed of what he sees as completing the anti-communist revolution of 1989, but he also knows, recalling his experience in power from 2005 to 2007, that the window of opportunity may not long be open. So he says to himself, like Macbeth, “If it were done … then ’twere well it were done quickly.”

Since what I have just written will be seen as partisan, unfair criticism by many who voted for Kaczyński’s party in last autumn’s election, let me state equally clearly what I am not saying. I am not criticising a party with a clear parliamentary majority for pushing through its proclaimed conservative, Catholic, Eurosceptic policies, cleverly combined with an almost leftwing set of economic and welfare promises. I may not like those policies, but that’s democracy. I have been for nearly 40 years now a friend of Poland, not just of one milieu, let alone of any particular party. Among my most moving memories is the vast crowd in front of the historic monastery of Częstochowa greeting Pope John Paul II in 1983, and singing the old patriotic hymn Return to Us, O Lord, a Free Fatherland.

PiS represents a whole conservative, religious side of Polish society and a solid third of the Polish electorate. Skilfully picking up other votes, benefiting from disillusionment with the centrist Civic Platform and pathetic chaos on the Polish left, it won a resounding victory in a free and fair election – like David Cameron’s Conservatives in Britain. So it’s not the policies, the politics or even the ideology that requires all friends of Poland to sound the alarm; it’s the winning team attempting unilaterally to change the rules of the whole democratic game.

A comparison with Tory-ruled Britain is interesting because PiS politicians claim to be implementing something like British-style parliamentary sovereignty. A British Conservative politician once described Britain’s political system as “elective dictatorship” because of the extraordinary power concentrated in the hands of any prime minister with a substantial and disciplined parliamentary majority. Yet although Britain does not have a written constitution, like the US and Germany, it does have powerful checks and balances: an impeccably neutral head of state; fiercely independent courts that do not hesitate to find against government ministers; the BBC; a professional civil service; security services that (these days, so far as I know) don’t do the bidding of one politician against other politicians; a robust culture of civil political debate … Need I go on?

In Poland, by contrast, the president, Andrzej Duda, is executing his political master’s strategy. Duda holds a doctorate in law, but his own doctoral supervisor says he has already violated the constitution three times. New legislation and judicial appointments will effectively neuter the constitutional court (formally constitutional tribunal); a new media law subordinates public service broadcasting directly to government; political appointees will be allowed at the highest level of the civil service, and so on. For a rough British comparison, imagine Nigel Farage in place of the Queen (King Nigel I?), Daily Mail editor-in-chief Paul Dacre appointed by the ruling party to direct the BBC, and Mail columnist Richard Littlejohn becoming the top official at the Foreign Office.

The good news is that Polish society is already mobilising in defence of liberal democracy. As early as last November, an opinion poll found 55% of respondents saying democracy is threatened in Poland. The EU has also responded more sharply than it did to similar (and worse) changes in Viktor Orbán’s Hungary. Tellingly, Kaczyński and Orbán met privately for five hours this week, coordinating their positions.

Next week, the day after Poland’s constitutional court meets to consider the constitutionality of its own emasculation, the European commission will discuss whether the attack on that court and the new media law justify invoking a new EU mechanism to defend the rule of law in member states. German media have given particular prominence to this dangerous turn in Poland – the European commissioner responsible for media also happens to be German, as is Martin Schulz, the outspoken president of the European parliament.

But if we leave it to Brussels and the Germans, it is all too easy for Kaczyńskiites to claim that Brussels is giving orders to Poland just as Moscow used to, and to play on still latent anti-German feeling. So we need traditional friends of Poland to speak up as well: its historic ally France, for instance (Poland is the only country I know to make positive reference to Napoleon in its national anthem); Spain, another major, traditionally Catholic country, which has made the transition from dictatorship to democracy; Italy; Canada. Not least, we should hear from the US, especially as Poland prepares to host an important Nato summit this summer and wants Nato forces permanently based in the country.

And what about Britain? Realistically, Cameron is the politician least likely to criticise Kaczyński at the moment, because he desperately needs a deal over in-work benefits for (mainly Polish) migrants in the UK, so as to win his referendum on Britain’s EU membership. But it’s worth putting Cameron on the spot, if only to hear his weasel words in reply. So will a British MP please challenge him about Poland in parliament at the next prime minister’s questions?