The world of conservative politics is full of such connections. After five minutes of affable banter about the Test match and other topics – for although Mr Farage’s office is cheerless, he himself is remarkably cheery – the interview began in earnest.

Mr Farage explained the coincidence: the donor, Andrew Reid, who provides him with this suite of offices, had previously given the same accommodation to Mr Johnson’s campaign.

Somewhat to my surprise, I found Nigel Farage, leader of UKIP, sitting in the same small, cheerless office, on the fifth floor of Moss House, a nondescript block behind Claridge’s, where in December 2011 I had interviewed Lynton Crosby, who now works for David Cameron but was at the time running Boris Johnson’s campaign for re-election as Mayor of London.

ConHome: “How in your opinion is he destroying the Conservative Party?”

Farage: “Let me give you an example of what Cameron is doing to Conservative voters in the south. The Eastleigh by-election: a result that the Daily Mail and others chose to say Ukip robs Tories of chance of winning Eastleigh. [On 28 February the Liberal Democrats held Eastleigh with 13,342 votes, followed by UKIP with 11,571 votes and the Tories with 10,559.] A mile and a half out of Eastleigh you get to possibly the finest trout stream in the world, the Itchen. The Test’s lovely but the Itchen’s even better in my opinion, and along the Itchen there are lovely villages trapped between Eastleigh and Southampton. It’s a bit of what’s left of Jack Hargreaves Hampshire, very traditional Conservative-type voters, very traditional, used to a Conservative Party that talks about aspiration, and talks about success and enterprise, and lowering taxes, and now has a Conservative Party that seems to prioritise, in this Parliament, gay marriage, building wind turbines, and making sure that while we sack 5,000 soldiers we keep our overseas aid the highest of any western country. Now you know, need I say any more? And some of them are horrified enough to come and vote UKIP, but lots of them just stay at home, can’t bring themselves to vote for anybody. Cameron disconnects completely with those people. At a social level, at an economic level there is no connection. And in the north of England, the Conservatives’ problem is even more serious. The Conservative Party is dying in the north of England, it’s disappearing.”

ConHome: “But isn’t this an argument for a new leader of the Conservative Party?”

Farage: “Let me finish. So in the north they’re dying, and in Manchester, and Sheffield, and cities like that they’re disappearing, not because of UKIP. A number of Conservatives have come across to UKIP, and a remarkable number since 2010.”

ConHome: “So what do you want to happen to the Tory party? Do you want to replace it? Do you want it to split apart? Obviously you can’t absolutely determine what happens to it, but what would be the best thing from your point of view? Because you are really the lost Tory tribe.”

Farage: “You wrote that years ago.”

ConHome: “No, no, I’m not claiming any originality. But particularly your activists and you yourself used to be in the Tory Party, and among the most energetic members. You revere Enoch Powell. You probably still think quite highly of Margaret Thatcher, despite the Single European Act. And many Tories want you back; think there should be a reconciliation. And there still seem to be some Tories you’re quite fond of. I’d quite like to have a complete list of the sheep and the goats, who are going to be cast into outer darkness, the insufferable ones from your point of view, people like Cameron.”

Farage: “He’s completely the wrong Prime Minister for now. Had he been the Prime Minister in 1958, at a time when consensus politics worked, because things were bumbling along very nicely, growth at three per cent per annum, the country just needed a bit of gentle management, needed someone on stage who looked cool and in command, he might have been fine, but if you’re Prime Minister at a time of great difficulty then you have to be radical, and I don’t think this chap’s got an ounce of radicalism in him.”

ConHome: “Well there’s the welfare stuff, there’s the education stuff.”

Farage: “Even the education stuff isn’t that radical. Radical would be a return to selection.”

ConHome: “A radical isn’t a very Tory idea anyhow. We shouldn’t be constantly radical. Radicals were the kind of people one didn’t have to dinner.”

Farage: “When the country’s in trouble you do need to be radical. Thatcher was radical. That was a radical government that did very radical things and whatever the downside was they made it a modern country where it was worth investing in car plants, the City. Just look at the immigration figures, the Government underestimated the number of people that came by the size of the whole city of Manchester, so I think if Cameron stays as leader up until the next election they haven’t got a cat’s chance in hell, and that’s regardless of whether UKIP’s there or not. I also think the effect of UKIP on the Conservative Party is more psychological than arithmetical, I really do. Some of the Ashcroft analysis after Eastleigh was really interesting. Ashcroft spent a fortune finding out who voted UKIP, why they voted UKIP. So a third of our vote in Eastleigh came from the Tories, a third came from the Lib Dems, 20 per cent came from old Labour and ten per cent came from people who hadn’t voted for anyone for 20 years. We didn’t cost the Tories that seat. And nationally, out of the people who say they’ll vote UKIP about four out of ten are Tories, so yes there’ll be marginal seats in which we may affect the Tory vote, but we’re hurting Labour just as much.”

It will be noted how intent Mr Farage is to deny that he is damaging the Tories. He also denied that UKIP’s vote has drifted downwards in recent months, and pointed out that UKIP does worse in polls where its name is not prompted. This interview was carried out before the Guardian’s ICM poll, analysed for ConHome by Paul Goodman, putting the Conservatives level with Labour on 36 per cent, with UKIP on 15 per cent.

Farage: “Our pollster, the chap who does our work for us, Survation, says that at 17 per cent, that’s the level at which we hurt the Conservative Party most, for every point above 17 per cent we then begin to hurt Labour, I think that’s entirely true and I think our potential in the Midlands and the North is huge, with the old Labour vote. I think as a party we must really focus our energies on that Labour vote. Miliband completely disconnects with working-class people. The immigration thing under Labour has been a complete disaster for working-class people, has completely changed their way of life, a lot of unskilled people can’t get jobs, a lot of skilled people have seen their salaries absolutely slashed, there is a huge well of ill-feeling. On the European question most working-class people make me sound like a Europhile.”

ConHome: “How do you hope to do in the European elections in 2014?”

Farage: “I’m aiming to win.”

ConHome: “And then get squeezed for the general election in 2015?”

Farage: “That may be true. Look, first-past-the-post is devilishly hard, and for us to win two things have to happen. First we have to do what the Reform Party of Canada did and that is to win a by-election. Second we have to win clusters of district and county council seats. The Lib Dems built up from about a dozen seats in Parliament to about 60 by building up local centres of excellence.”

ConHome: “Are you also hoping for Tory defections?”

Farage: “Do I spend my life thinking about defections? No. We’re building our own brand.”

ConHome: “I don’t like the word ‘brand’.”

Farage: “It’s absolutely vital.”

ConHome: “No, it’s like breakfast cereal or something. The future of our nation cannot be discussed in these terms.”

Mr Farage retorted that under Mr Cameron, “we have no future as a nation”. He observed that on the same day as next May’s European elections over 5,000 local council seats will be contested, “so the voter gets two ballot papers and I’m going to urge them to vote UKIP twice,” which will show “where our real geographical strength is…my thinking would be we go into 2015 and throw the kitchen sink at them.”

It is Mr Farage’s belief that by 2015 “Miliband will have promised a referendum” on Europe, so the argument for voting Tory in order to get one will no longer apply.

ConHome: “What about Boris as leader?”

Farage: “That would be fun. I’m not sure where he is on policy. Although I think his general instincts are the right ones.”

ConHome: “So he’d be a tougher opponent for you?”

Farage: “I think if Boris was Tory leader it’d make my life much harder, yes. Boris says things that lots of UKIP voters have said before him. If any kind of deal was to be done, which is absolutely not my priority, the current Tory fantasist idea that UKIP will just pack its tents and disappear, forget it, that is not going to happen. But what would be the prerequisites for some kind of deal? Number one the right kind of leader who wasn’t consistently rude about us, and maybe someone like Gove would think about things more, and be slightly more respectful of the point of view UKIP take on a range of issues.

“And it would have to be an electoral pact of a kind that either went down the joint candidacy route in some constituencies, you know the Jacob Rees-Mogg idea, which I’ve always said I’d be open-minded to, I have not slammed the door in the face of that as a possible idea, or it would be a simpler ‘we fight this number of seats and you fight that number of seats’. Those to me are the two possibilities.”

ConHome: “How many Tories at present have you said you won’t fight at the next general election?”

Farage: “We didn’t fight about ten last time round, but at the moment I haven’t committed us at all on that.”

ConHome: “It would be odd if you fought people like…”

Farage [interrupting before any examples can be given]: “Well that’s always been my view, but, you know, I might lead UKIP but I absolutely can’t tell the branches what to do, there’s a very strong grassroots element to this party, there really is. Do I think a deal will happen? I doubt it, I think the Tory Party will stick with Cameron.”

ConHome: “You’ll probably stand in 2015?”

Farage: “I think so. I think 15 years of Brussels is enough. Where our target seats will be will very much be determined by socio-economics.”

ConHome: “Your voters tend to be somewhat less prosperous?”

Farage: “Yes, absolutely. You can’t tell from the house whether they’re Labour or Tory. And a lot of our voters are disengaged. Your classic profile is retired Londoner, living in Worthing, family was Labour, backed the Tories when Maggie was leader. There are a lot of them out there in those seaside towns. Most UKIP success is on the seaside. You look at it. Boston [Lincolnshire] we’re very strong. Great Yarmouth: huge successes in Great Yarmouth. Thanet, which is an island. And, yes, along the Sussex coast. We are the seaside party. And Eastleigh. Eastleigh was virtually seaside, next to Southampton. And South Shields [where in the by-election in May, Labour got 12,493 votes, UKIP 5,988 and the Tories 2,857]. Postal votes. It’s going to become very difficult for anyone who holds a seat to lose a by-election. South Shields. What a joke. They gave David Miliband a safe seat. They called a by-election at literally the constitutional minimum of 20 days. 58 per cent of the turnout in the by-election was postal vote. From the moment the by-election was called to the ballot papers going through the doors was a matter of days. We couldn’t canvass them. And despite that we got 25 per cent of the vote, having never stood in South Shields before. South Shields was actually more remarkable than Eastleigh, astonishing, and that was all old Labour. In the north they’re coming to us. It’s very interesting. It’s actually rather exciting. But the thing I love about this now is we’re not a Tory splinter group. We were in the early days.”

ConHome: “You’re married to a German. What do you make of German euroscepticism?”

Farage: “The Germans are trapped. If the euro goes down the tubes the Germans are down a trillion euros, a third of their annual GDP has gone. It’s politically impossible for the euro to break up: the Germans cannot allow this to happen. So I suspect what will break up the eurozone will be violence on a large scale in the Mediterranean. I don’t see any other solution to this, I really don’t, I’m very very very pessimistic about the social situation in some of those countries.

“France is probably the most fascinating of the lot. Marine Le Pen [leader of the Front National] is doing very well, she’s doing remarkable well, which makes life difficult for us in some ways. We’re not going to touch them with a bargepole. Anti-semitism is written into the DNA of that party.”

Mr Farage does not employ a gatekeeper to stop people getting through to him, and as the interview went on it was more and more often interrupted by the ringing of his mobile phone. He makes a speciality of being available: when I requested this interview, he suggested we meet in half an hour’s time in the Marquis of Granby pub in Westminster.

That was not possible, but once our talk in his office was over, we went for a drink at the Guinea pub in Mayfair. Mr Farage was greeted with striking enthusiasm by a number of complete strangers who wished to buy him drinks and have their photograph taken with him. One doubts whether any leader of a political party has ever felt so at ease in the pub.