Promises made in the leaked Labour manifesto will set the UK on "the road to ruin", according to the Tories.
The content reveals the party to be in "utter chaos" on Trident, the SNP said, while Plaid Cymru said it shows Labour to be "weak and divided".
But the details will be unsurprising to most, Ben Page, chief executive of Ipsos MORI said, adding that the leak was unlikely to affect people's views on Labour.
"People have made their mind up, pretty much, about Jeremy Corbyn," he told BBC Radio 4's Today programme.
"They know what to expect from the Labour Party under Jeremy Corbyn.
"There are some things in there that have a constituency, but for most people I think there isn't going to be a huge surprise."
Defence Secretary Sir Michael Fallon said hiking taxes for people earning the biggest salaries could drive businesses out of Britain.
And he claimed the plans would require a "massive borrowing spree".
He told Good Morning Britain: "Lots of promises, a fairly shambolic launch. They probably didn't plan it that way, but lots of promises in there to spend lots more money on lots of different things.
"What they have not made clear is how that is going to be financed, how much more borrowing there's going to be and what the implications are for the economy if you go on a massive borrowing spree like the last Labour government did.
"That's how we got into the mess that we inherited back in 2010 and that's what's not made clear in Labour's manifesto today. They would borrow more and that in the end is the road to ruin."
He added: "You'll see when it comes to our manifesto - and only a few more days to wait for that - you'll see in our manifesto the specific pledges of how we're going to spend on the National Health Service, spend on social care, and the things that people really need public money spent on.
"But you don't do it by simply taxing businesses to the point where they leave the country."
The SNP's Glasgow North candidate, Patrick Grady, said: "This leak confirms Labour are in utter chaos over Trident - with the party in Scotland and Jeremy Corbyn diametrically opposed to what's in their manifesto.
"Now more than ever, it is vital to have strong SNP voices standing up for Scotland, speaking out against weapons of mass destruction just a few miles from our largest city.
"With Labour in disarray only the SNP can protect Scotland from the dangers of a Tory government at Westminster."
Tom Brake, the Liberal Democrat foreign affairs spokesman, said: "This manifesto became meaningless the day Jeremy Corbyn ordered his MPs to vote with the Conservatives and Ukip to give Theresa May a blank cheque on Brexit.
"Labour supporters should have hope that someone will stand up to Theresa May's divisive Brexit deal, but it won't be Jeremy Corbyn.
"Another option is available. The Liberal Democrats will stand up for you, your family, your schools and hospitals and give you the final say on Brexit, with the choice to remain if you don't like the deal on offer."
Plaid Cymru's Jonathan Edwards said: "In the face of a Tory landslide at UK level, that elements of Labour's high command are more focused on damaging their leader by undermining their own manifesto than they are on opposing the Tories, shows the chaos within the Labour Party.
"Many of the policies in the leaked manifesto are policies that the Labour Party has opposed and blocked in the Welsh Government.
"They say they want to scrap tuition fees but continue to charge £9,000 in Wales where they govern.
"They say they want to scrap zero hour contracts but have voted against doing so on seven separate occasions despite having the power to do so in Wales.
"The only thing we have learnt from this leak is that Labour is too weak and divided to stand up to the Tories and defend Wales.
"Wales needs a strong and united group of Plaid Cymru MPs to give the Tories the opposition this country desperately needs."
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