Surprisingly, it’s not just ambitious Tory MPs with dreams of ministerial office who will be waiting by their phones the day after the General Election if David Cameron becomes Prime Minister. The maverick Labour MP Frank Field, who has had turbulent relations with Tony Blair and Gordon Brown, may also receive a call.

During Mr Field’s 30 years as an MP, hundreds of ministers have come and gone – few are remembered. Field himself was a minister for only 18 months in Tony Blair’s first government. But far from being an also-ran, he is now – at the age of 67 – at the peak of his powers. More pertinently, he is one of only a handful of politicians in Britain with the courage to break the cross-party silence on immigration and propel it to the centre of the political stage.

With a rock- solid Merseyside seat, and a thick skin after three decades in public life, he doesn’t care who knows that he thinks Mr Brown is a disaster who should never have been Chancellor, let alone Prime Minister. They repeatedly clashed when he was the minister charged by Mr Blair with ‘thinking the unthinkable’ on welfare reform back in the days of the first New Labour government.

So, with no chance of a return to office under Labour, what about serving David Cameron, who has pledged to mend ‘Broken Britain’ by radically overhauling the benefits system? ‘If the Tories want to talk to me about a job, I will be happy to,’ says Field. ‘My door is open to any party to develop ideas. Tory, Liberal, or my own. I will always put the interests of my country and constituents before my party. I have never refused to speak to people on the other side.’

Pressed on whether he would take a ministerial job, he says: ‘I would love to be asked by the Prime Minister, especially my own, to take on a role to help convince the world we are serious about our debts, getting immigration under control, and reforming welfare. I am up for that challenge.’ So why not talk to our current PM? ‘I would love to talk to him,’ says Field, ‘but he won’t speak to me.’

Mr Field tips the scales at barely 11 stone, the same weight as when he was first elected, yet he never goes to the gym. He eats too much, and likes red wine. He rarely watches TV or goes to the theatre. He prefers to relax by reading political tomes such as the latest biography on Churchill. He represents one of Labour’s safest seats, Birkenhead.

Even 20 years after the fall of Margaret Thatcher, she is still a hate figure among swathes of his electorate. Yet long before Mr Brown also professed his admiration for her, Field was hugely impressed by the woman he thinks was the most radical British leader since Clement Attlee’s post-war government, which created the NHS. ‘I have a good relationship with her. She has become much nicer as she has got older. In fact, I’m having coffee with her tomorrow.’ His late father, a building labourer, and mother, a classroom assistant, would approve. They voted Tory.

Mr Field makes no apologies for being willing to talk to the Tories. His mission has been to create a Labour Party that speaks to ordinary working people, gets the poor off benefits, reduces state spending, and has full employment as a goal – admirable objectives, which his party has failed to achieve. So if the Tories can achieve them, he will engage with them….

It’s inflammatory stuff for a Labour MP. But by his own admission, Field is a serial rebel in the Commons. ‘On issues I really know about, I sadly usually disagree with the Government. For that reason, I try not to find out about the other issues so I can put in a reasonable number of votes on behalf of my party.’ …

But it was his decision to set up Balanced Migration, a cross-party political group to campaign against mass immigration, which has thrust him to the fore once more. According to government statistics, one immigrant arrives every minute, and a new British passport is issued every three. In the past ten years, almost 750,000 British people have left the country, and 2.5 million immigrants have arrived. The rate of inflow is 25 times higher than any previous period of immigration since the Norman Conquest.

Last month it emerged, under the Freedom of Information Act, that far from being unexpected, this massive increase was sanctioned by the Blair Cabinet – not least to ensure a strong backing for Labour from the new immigrants at successive elections. ‘You can count on less than two hands the number of brave Labour MPs who have said we have to stop growing our population by immigration,’ Field says. ‘For his part, David Cameron has proposed a cap on immigration. He must put a figure on that.’ Field proposes cutting it to 30,000 a year from 90,000. ‘When people who have worked all their lives are unemployed because of the recession, we can’t continue to have free movement from the countries that have recently become a part of the European Union. We have to withdraw temporarily from that.’

He warns that unless British people are put first, the Government risks serious outbreaks of civil unrest on a scale similar to the inner- city race riots that took place under Thatcher’s first administration. ‘It’s like a drought. The tinder is very dry across Britain, particularly in areas which are most up against it. Despite what politicians say, the NHS and education budgets will all be cut. ‘Yet schools will have to find new classrooms and teachers because we continue to grow our population through immigration.

‘Parents know their children are not achieving what they might, despite unimaginable increases in the education budget, because teachers are disproportionately trying to make sure the new arrivals catch up with everyone else.’

The flashpoints could come in cities such as Bradford and in East London where the BNP is seeking to capitalise on simmering unrest among workingclass whites. ‘The migrants come here and then people get nasty because they have created their own local villages in the inner cities. The charge sheets for this should be laid against the political elite who allowed this. ‘The headlines will be dominated in the next few years by how we survive financially. Yet we won’t survive longer term unless we put down the foundations for a new citizenship. ‘And that must start with the fundamental truth that until you fulfil duties as a citizen there can never be anything such as rights. You should only get rights to benefits, for instance, if you have paid your contributions.

‘We should ensure that the people who come here to work don’t then have 300 members of their families who want to come, too. I don’t think the British voters are going to put up with this for much longer. ‘There is a risk of civil unrest. We have to turn off the immigration tap, so we can say to people: “You haven’t trusted us in the past, but we are at least not going to make it any worse.” ‘

As the polls point to the closest election fight since 1992, Mr Field is clear that although he might consider an approach from a Cameron government, he wants Labour to win. Even under Gordon Brown? ‘I am looking forward to the election of a Labour government,’ he says. Yes, but what about Mr Brown personally? ‘I want to see Labour win,’ he repeats. With Mr Brown at the helm? ‘I want to see a Labour PM.’

His point is clear. Indeed, not only will he not endorse Mr Brown as PM, he has already identified his favoured candidate if there is a change of leader after polling day. ‘If we have to look for a safe pair of hands, Alistair Darling has quietly put himself into the ring. He is quietly authoritative and has stood up to Brown.’

Frank Field predicts that the country is about to enter its stormiest waters since postwar reconstruction in 1945. ‘I am not sure the country will necessarily be OK. But a country that was able to stand alone and beat the Nazis must have enormous inner reserves. We’re going to need them.’