There is a massive need for facts, numbers, explanations and reassurance to be restored to the immigration debate

No western European country can afford to pretend that the prospect of migration from new EU member states raises no domestic economic or political issues at all. But politicians in such countries should not whip up falsely based fears about the scale and nature of such migration either.

Countries like Britain have a responsibility to raise and discuss these issues objectively, responsibly and honestly. That has not been happening in this country as the 1 January date for the lifting of labour migration restrictions on Bulgarians and Romanians gets closer. Quite the contrary.

In recent weeks, David Cameron seems to have abandoned all efforts to put facts not fears at the centre of the argument or to make a case for necessary immigration in the modern world. Instead he has been acting as though millions of Bulgarians and Romanians will be queueing for entry as soon as the restrictions are lifted, confident that they will spring to the top of the jobs, housing and welfare queues.

His government has rushed through a series of changes to the welfare system (some of which are in fact more cosmetic than they seem) and has threatened to block new EU members – such as Serbia, Ukraine and eventually Turkey – unless major curbs on freedom of movement within Europe are imposed.

All this gives the impression, as the president of Bulgaria rightly said in an Observer interview on Sunday, that Mr Cameron is pandering to nationalism and is willing to isolate Britain.

Voters' anxieties are a reality – look at the polls if you doubt it – and are bound to be greater in difficult economic times. They must obviously be answered. But Mr Cameron is not doing that at all. Instead he appears to be running scared of the lies of the rightwing anti-foreigner press, of the rise of the Ukip balloon, and of the nastiness of his own most xenophobic backbenchers.

Mr Cameron is not displaying anything approaching the level of leadership that is required of a responsible prime minister on these issues. A few Conservative MPs have behaved responsibly. In the main, though, it has been left to the Liberal Democrats to stress that pulling up the drawbridge by imposing an EU migration cap would be illegal, undesirable and unworkable.

Nick Clegg and Vince Cable both gave principled interviews to the media on these issues on Sunday. They are right to challenge the anti-immigrant panic before it gets worse, which it surely will as January nears.

There is a massive need for facts, numbers, explanations and reassurance to be restored to the immigration debate. But that's easier said than done. The Lib Dems cannot be expected to win the argument on their own.

Clearer and more confident voices from the Tories and Labour should join them. At present, too many of their heads are being kept down for tactical reasons.