Nigel Farage today conceded that he could get six million votes on July 4 and still only have a 'paltry' number of MPs.
The Reform leader painted himself as the 'opposition' to Labour, after one poll showed his insurgents with more support than the Tories.
But at a press conference in Westminster, Mr Farage admitted that the electoral system made it very hard for parties to break through and win seats.
He said he hoped Reform would get significantly more than the 3.9million votes Ukip received in 2015, despite not having 'ammunition' or an established 'ground game'.
'If we did finish up with a huge number of votes and a paltry number of seats, do you know what it would do?' Mr Farage said.
'It would tell us yet again that Britain is broken and Britain needs reform, and that reform includes the electoral system, that reform includes the abomination that is the House of Lords, and that reform includes the right, as people in Switzerland have, to call referendums on key issues if they think their government and parliament are out of touch with them.'
The comments came as Rishi Sunak tried to calm Tory nerves over the YouGov research finding that Reform had leapfrogged the party.
The PM urged voted to focus on who should be in No10 between him and Keir Starmer, warning that even if the findings came to pass it would only hand Labour a 'blank cheque' to hammer Brits with more taxes.
The first past the post system means that new parties often gain a spread of votes across the country - but support is not concentrated enough to win constituencies.
Nigel Farage conceded that he could get six million votes on July 4 and still only have a 'paltry' number of MPs
Rishi Sunak tried to calm panicky Tories today after a poll showed a 'crossover' moment with Reform leapfrogging the party
The PM urged voted to focus on who should be PM between him and Keir Starmer , after YouGov research put Nigel Farage 's insurgents in second place
Although it is just one survey and had been widely anticipated, the YouGov figures have fueled anxiety within Conservative circles about the campaign.
Asked if he was despairing that Reform UK is now polling ahead of the Conservatives, the PM told reporters at the G7 summit in southern Italy: 'We're only halfway through this election, so I'm still fighting very hard for every vote.
'And what that poll shows is - the only poll that matters is the one on July 4th - but if that poll was replicated on July 4th, it would be handing Labour a blank cheque to tax everyone - tax their home, their pension, their car, their family - and I'll be fighting very hard to make sure that doesn't happen.
'And actually, when I've been out and about talking to people, they do understand that a vote for anyone who is not a Conservative candidate is just a vote to put Keir Starmer in No 10.
'So if you want action on lower taxes, lower migration, protected pensions or a sensible approach to net zero you're only going to get that by voting Conservative.'
Pressed on whether he needed to find a more effective way to counter the threat from Nigel Farage's party, Mr Sunak said: 'So we're only halfway through this and when I'm out and about talking to people, people do get that utimately, if you're not going to vote for a Conservative candidate that makes it more likely that Keir Starmer's in number 10.
'And when people are thinking about the substance of what they want to see from a future government, if you're someone who wants to see control over borders, you're going to get that from us. You're not going to get that from Labour, they're going to cancel the Rwanda scheme, they're not going to put in place a legal migration cap.
'If you want a sensible approach to net zero, I've already announced that. Labour would reverse those reforms and put everyone's bills up with net zero costs. And if you want your pension protected, we're the only ones offering a triple lock plus.
'So actually, when people sit down especially now this week when everyone can see very clearly the difference in approach from the two parties, I think that choice will crystallise for people between now and polling day. We're only halfway through.'
And asked if the election was an existential one for the Tories, he said: 'I think at the end of the day on July 5, one of two people's going to be Prime Minister - Keir Starmer or me - and this week the most important thing that happened was you saw both major parties manifestos, that's their programme for government if they were elected.
'So now everyone has a very clear sense of what each of us would do and as you saw from our manifesto, as we were discussing yesterday, say what you want about it, but it's a very clear plan, a detailed set of bold actions. That's how you deliver a more secure future for people and crucially, there's a massive difference on tax.
'We want to cut your taxes at every stage of your life in work, setting up a business, buying your first home, when you're retired, you're a pensioner or if you have a family cutting taxes for everybody.
'The Labour party consistently can't tell you which taxes they're going to put up but they are going to put them up and as we saw yesterday, they're going to raise the tax burden to the highest level in this country's history. And that's the choice for everyone at the election.'
Mr Farage told BBC Breakfast his campaign had enjoyed a 'phenomenal start'.
'Back in 2015 when I led Ukip into a general election, we got 4million votes and one seat – never before had anybody got so many votes for so little reward,' he said.
'But we're looking this time at many, many more votes than 4million, we're hoping to get through the electoral threshold. Whatever we do, we may not get the number of seats we deserve, but are we going to win seats in Parliament? Yes.
'How many? There's three weeks to go, we've got momentum behind us and there's three long weeks to go.'
Pressed to outline a target, Mr Farage replied: 'I have no idea. The Labour Party are massively ahead in the polls, the Conservative Party has not bounced one little bit in these first three weeks, they're not going to.
'And my message is very simple – that (Labour leader Sir Keir) Starmer is going to have a very big majority, I don't think he has much of a plan, his six priorities didn't even mention legal migration which is a huge issue, so I want us to become the opposition voice in Parliament and in the country. That's the ambition.'
The YouGov poll has taken attention away from the Tories' efforts to nail Labour over tax plans after Sir Keir unveiled his manifesto yesterday.
The document laid out plans to boost the burden by £8.5billion to pump money into services, but although promising no change to income tax, national insurance and VAT Sir Keir has refused to rule out moves on council tax and capital gains.
The left-wing Resolution foundation warned last night that the proposals set the stage for five years of tax rises and public service curbs, amid widespread criticism that none of the parties are being honest about tough choices the country faces.
At a press conference this morning, Treasury minister Laura Trott tried to renew the attack, saying Labour had 'deliberately failed to rule out 18 potential tax rises'.
'What's most important about Labour's manifesto is what is not in it,' she said.
'Not including planned tax increases in manifestos is standard practice for Labour… We don't want Labour to get away with it this time.
Ms Trott said the Reform poll was a 'stark warning' to voters. 'The Conservative Party are fighting for every single vote in this election,' she said.
'And look, we're only halfway through, right? Things can change.
'But the poll is a stark warning. If a result like this is replicated on election day, Keir Starmer would have huge and unchecked power to tax your home, your job, your car, your pension however he wants.'
The think-tank said: 'Their current stance sets the scene for a Parliament of further tax rises, hard to deliver spending cuts, and the risk that a weaker productivity forecast from the OBR at the next fiscal event could force an incoming Labour chancellor into fresh hard choices in order to meet their stated fiscal rule of getting debt falling by the fifth year of the forecast.'
Labour's pledges to increase public spending largely lie in departments that are already protected, such as health and social care and education, the Resolution Foundation said.
The YouGov poll has taken attention away from the Tories' efforts to nail Labour over tax plans after Sir Keir unveiled his manifesto yesterday
Paul Johnson, director of the Institute for Fiscal Studies (IFS), suggested that delivering 'genuine change' in Britain – Sir Keir Starmer's flagship promise to voters – would require more funding than the policy document proposes.
Mr Johnson said some of Labour's plans were better than 'a shopping list of half-baked policy announcements' – an apparent reference to the Tories' offering – but warned it would need to put 'actual resources on the table'.
'And Labour's manifesto offers no indication that there is a plan for where the money would come from to finance this,' he said.
In a response to Sir Keir's launch of the policy document on Thursday, the IFS director said: 'This was not a manifesto for those looking for big numbers. The public service spending increases promised in the costings table are tiny, going on trivial – the tax rises, beyond the inevitable reduced tax avoidance, even more trivial.
'On current forecasts, and especially with an extra £17.5 billion borrowing over five years to fund the green prosperity plan, this leaves literally no room – within the fiscal rule that Labour has signed up to – for any more spending than planned by the current government, and those plans do involve cuts both to investment spending and to spending on unprotected public services.'
Mr Farage has gloated that he is now in charge of the main opposition, hammering home the point in an ITV debate nast night and interviews this morning.