LONDON • Mr Boris Johnson, a former London mayor and lead campaigner for Britain's exit from the European Union (EU), has called for an amnesty on long-term illegal immigrants already settled in the country.

The proposal, made ahead of Thursday's crucial vote on Britain's continued EU membership, is designed to deflect accusations that Brexiters - as supporters of Britain's exit from the EU are popularly known - have used crude anti-immigrant and racist slogans to pollute the political debate during the EU referendum campaign and may have even indirectly inspired last week's murder of Mrs Jo Cox, a local opposition MP and fervent migration defender.

But Mr Johnson's attempt to reject racist labels appears to have backfired, as Mrs Sayeeda Warsi, a former chairman of the ruling Conservatives and one of Britain's leading ethnic minority politicians, announced she is defecting from the Brexit camp because of the "hate and xenophobia" of their campaign.

Still, it is by now clear that the outcome of Britain's EU referendum will be decided later this week largely on the basis of voters' opinions on border controls and immigration.

For decades, the main sources of Britain's migration remained the former British colonies, and particularly from the Indian subcontinent.

All this changed in 2004, when the East European nations joined the EU, generating a large inflow of workers which has now boosted the number of EU citizens settled in Britain to around 3.1 million, or around 4.8 per cent of the total population.

Many of the scare stories generated by the British media about this migration wave are myths. The migrants are not a burden on Britain's health services; they are mostly young, so they hardly use the medical services for which they pay. Not all of them come from poor East European countries: Surprisingly, the third-largest group of EU migrants in the UK comes from Germany, Europe's wealthiest nation. And although some are unskilled, EU workers are better trained than many in the British labour force.

Still, the fact that the number of migrants has climbed so fast and that the British government is powerless to stop it have provided perfect ammunition for Brexiters, who argue that only by leaving the EU would Britain be able to "take control of its borders", as one of their electoral slogans currently puts it.

Brexiters knew from the start that they were vulnerable to accusations of racism, and they tried their best to deflect them. Ethnic minority figures such as Mrs Warsi or Mrs Priti Patel, Britain's current Employment Minister and the first Hindu woman to be elected to the British Parliament, were put forward to argue the case for withdrawal from the EU.

And the Brexiters even managed to turn the accusations against their enemies, by charging that those who wish to keep Britain in the EU are the "real racists" for they are giving priority to Europeans at the expense of migrants from beyond the continent.

The tactic worked: All opinion polls indicate that most of the popularity gains notched by the Brexit camp during the current referendum campaign came as a result of their use of the immigration card.

But last week's decision by the far-right UK Independence Party (UKIP) to unveil a campaign poster showing a large queue of non-white refugees under the caption "Breaking Point" has transformed the debate. Its racist message was clear: If you don't want your communities swamped by brown people, vote to leave the EU. And UKIP's association with the Brexit umbrella organisation was unmistakable.

The assassination of Mrs Cox has added another sinister element: Although the motives of her murderer are yet to be revealed, it is increasingly clear that the tragedy is connected to the climate of hatred against foreigners which now permeates the EU referendum debate.

Mr Johnson's call on the British government to consider an amnesty for illegal immigrants is being widely dismissed as just a gimmick to deflect attention from the real problem, which is the intemperate and aggressively anti-foreigner tone of the debate.

And that may well hurt the Brexiters, partly because accusations of racism put them on the defensive in the last days of campaigning, and partly because this may encourage Britons who did not care very much about the referendum to go out and vote on Thursday; all opinion polls indicate that the higher the voter turnout, the higher the chances for the defeat of the Brexit camp.

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From Great Britain to Little England

•More reports on Britain's EU referendum online at http://str.sg/brexit