David Cameron has defended the Union between England and Scotland, while the SNP says it is "increasingly optimistic" that is can secure independence.

The Conservative leader was in Scotland on Monday to meet Scottish Tory chief Annabel Goldie, before speaking to party members in Edinburgh.

Ahead of his speech, the Sunday Telegraph published a poll showing that more than six in 10 of English voters say they feel British, and 69 per cent want to keep the Union between England and Scotland.

And Cameron told the Daily Telegraph on Monday: "It's worrying that the Union is under strain.

"There are tensions, but it's often because people see that free medicines are available in Scotland and not in England for example. I would say don't blame the Union for that, blame the way the NHS is run. It's been mismanaged.

"I very strongly believe in the Union and it's important not to threaten it or undermine it."

Meanwhile Alex Salmond is set to say he is "increasingly optimistic" that voters will back independence within four years.

The SNP on Monday published a poll showing public support for the the minority government's spending plans, with 45 per cent describing them as good and 17 per cent as bad.

Asked who they would trust with Scotland's economy and finance, 31 per cent chose Scottish finance secretary John Swinney, and 13 per cent chose chancellor Alistair Darling.

According to the YouGov poll, 41 per cent of respondents said they trusted neither.

Asked to compare the performance of the SNP government at Holyrood and Labour at Westminster, 54 per cent said the Scottish government was doing the better job, while 11 per cent said the UK government was.

In a speech in Edinburgh on Wednesday, first minister Salmond is expected to say: "We are asking the big questions about Scotland's rights and responsibilities, and offering our vision for Scotland in the European Union and wider world.

"I am increasingly optimistic that there will be a referendum on Scotland's future in the term of this Parliament - and that the people of Scotland will vote for independence and equality."