Conservatives are now a party of English Nationalists, says Brown

The former prime minister claimed the Tories had sacrificed their traditional support for the Union to pursue a "divide and rule" strategy that has boosted support for the Nationalists.

He hit out in what is expected to be his final major speech of the campaign, delivered as he accepted an honorary doctorate at Glasgow University.

The Tories have issued increasingly lurid warnings about the prospect of a minority Labour government propped up by the SNP, despite Ed Miliband's assertion he will not do a deal with Nicola Sturgeon.

In one Tory poster, Alex Salmond was depicted as a pickpocket.

An Ipsos Mori poll yesterday suggesting the SNP would take every seat in Scotland - the most dramatic prediction yet - only reinforced the notion that Tory tactics are galvanising the nationalist vote.

Mr Brown angrily denounced Mr Cameron for fighting an anti-Scottish campaign that he said has turned the election into a battle between English and Scottish nationalism.

He found an unexpected ally in Andy Maciver, a former Scottish Conservative press chief, who said Mr Cameron's tactics were "poisonous" for Tories north of the Border.

Writing on the influential Conservative Home website, he said Scots Tories were "increasingly being hindered by their association with London" and claimed senior party figures were "livid".

Another poll yesterday suggested the Tory campaign was having an impact in key marginal seats in England.

The ComRes snapshot showed that in the 50 most marginal Tory-held seats, 58 per cent of people were worried about the influence Nicola Sturgeon and her colleagues could have on an Ed Miliband government.

Indeed, 47 per cent made clear the Nationalists should be "kept out" of a UK government while 62 per cent felt a Lab-SNP alliance would not be good for Britain.

Mr Brown singled out Mr Cameron's "Carlisle Principle" - the Prime Minister's proposal for an report on Holyrood decisions that have impacted adversely on the rest of the UK - for particular criticism.

He claimed it threatened the Scottish Parliament's powers and "hammered a further nail into the Union".

Slating Tory posters showing Ed Miliband in Nicola Sturgeon's pocket, he said: "There should be no doubt what lies behind the supposed appeal of the poster to the English people.

"It is an attempt to warn of a 'Scottish menace' and it can only work by fomenting anti-Scottish sentiment in England."

He said Mr Cameron "has been using Scottish nationalism to incite English nationalism" to avoid fighting the election on his record in government over the past five years.

He added: "This tit-for-tat policy to divide and rule sweeps aside what binds us together in favour of emphasising what drives us apart.

"The Government of the day has stopped speaking up for the Union they claim to support.

"Indeed the Conservative and Unionist Party has sacrificed its historic commitment to being a Unionist party to become an English Nationalist Party."

He accused Mr Cameron of lacking statesmanship, adding:

"The question is now not where stands Britain but whether Britain will stand at all.

"It for the Scottish people to judge whether with their anti-Scottish campaign have surrendered the claims to be electable again in Scotland."

Mr Brown warned Scots against confusing nationalism with patriotism.

He argued that social and economic problems "which give birth to nationalism cannot be solved by nationalism."

Repeating a message he sent at the weekend, he said: "Commentators equate patriotism with nationalism but I see most people in Scotland like me, as proud patriots who want change and fairness. "These are long-term aspirations the Labour party will prove best able to represent."

Mr Brown said the SNP privately wanted a Conservative government in the belief it would fuel support for independence.

Nicola Sturgeon rejected the claim earlier in the day when she told a meeting of business women she was campaigning to "lock the Tories out of government".

She added "I do think it is wrong that throughout many years of my lifetime we've had Tory governments govern Scotland with perhaps one or zero MPs in Scotland.

"So, this time, let's try and be part of getting them out completely but then using our voice to make sure they are replaced with something better, not with a Tory-lite government but with a progressive, bold and better government. That's where SNP MPs can have a big, big influence."

At the weekend, Home Secretary Theresa May questioned the legitimacy of a possible Labour-SNP alliance, claiming it could lead to the biggest constitutional crisis since the abdication of Edward VIII in 1936.

Mr Brown's comments were echoed by shadow chancellor Ed Balls, who said: "The idea that the supposedly Unionist party is talking up the Nationalist Scots to try and set Englishness against Scottishness is one of the most reprehensible things I've seen in modern British politics."