We mentioned a little earlier that David Cameron is to announce plans for an annual review of Scottish devolution to ensure the rest of the UK does not "lose out", if his party wins power on 7 May. Here's our story.

BBC News Channel

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The general election is not about independence, says Stewart Hosie. "We're not seeking a mandate for independence and this isn't a re-run of the referendum." This is about holding Westminster to account, and strengthening Scotland's voice and ending austerity, he explains.

BBC News Channel

If Labour and the SNP entered into a confidence and supply arrangement with Labour "clearly we couldn't agree to spend £100bn on Trident", says SNP deputy leader Stewart Hosie.

"If on the other hand this was done on a vote by vote basis we would be at liberty to support those things which are good, to strengthen policy where we could and of course quite normally, naturally to oppose these things we disagree with as every other party in Westminster does," he adds.

Mr Hosie deftly sidesteps a "yes or no" question on whether the SNP would let a Labour government collapse over Trident. Rather he flips it around, and asks if Labour leader Ed Miliband is prepared not to speak to the SNP and hand power back to David Cameron. "I suspect he doesn't want to be the hand maiden of another Tory government and neither do we", he adds, and calls for "sensible discussions about how we do the best thing for all of the people on these islands".

There are many ambiguities in the Fixed Term Parliament Act - very well explained by Dr Catherine Haddon, from the Institute for Government, external. One point she makes is that Budgets and Queen’s Speeches have long been viewed as effectively votes of confidence - fail to get either of those passed and you’re in trouble. But the FTPA has been defined narrowly to exclude both of them - the Commons must now pass a motion with very specific wording to trigger FTPA.

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BBC News Channel

SNP deputy leader Stewart Hosie tells the BBC the party will vote against any move in the next parliament to maintain Britain's Trident nuclear weapons programme, but insists it won't be holding defence "to ransom", as the party wants "a proper, strong conventional defence force".

So you would block specific government spending if it didn't suit your purposes, he is asked. That's they way the system works, Mr Hosie responds, saying the party would work to deliver what it believes is in the best interest of the whole of the UK. This isn't about bringing governments down, he goes on to say, but about "strengthening government and making it better".

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We mentioned the Fixed Term Parliaments Act in an earlier post - but what is it?

Well, it was introduced by the coalition in 2011 as part of the agreement for government drawn up by the Tories and Lib Dems in the wake of the 2010 general election. Under its terms, parliamentary elections must be held every five years.

An election could only be triggered before that if a motion of no confidence was passed in the government and no alternative administration could be formed, or if at least two-thirds of MPs approved calls for an early election.

Previously it was up to the prime minister of the day to choose when to call an election, provided it was within five years of the last one being held.

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BBC Radio 4 Today

On to defence now, and John Swinney is asked whether the SNP would rather force a second election than support a government which spent money on maintaining Trident? Mr Swinney does not accept the premise of the question, saying the fixed-term parliaments legislation means a government would not collapse on the basis of budget decisions.

Today programme presenter James Naughtie contends that there is nothing to prevent the fall of a government - and repeats his question. But it looks like the two men aren't going to agree. Mr Swinney says the party will vote to make sure conventional defence forces are "properly funded" - and is told he's avoiding the question.

The Scottish deputy first minister thinks otherwise.

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BBC Radio 4

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Scotland's deputy first minister John Swinney tells Today why the SNP will seek to influence decisions at Westminster that are devolved to Scotland, in the next parliament. Mr Swinney says there re policy changes taken at a UK-level which impact on the affairs of Scotland, such as NHS spending. That is a justification for us advancing our policy interests at Westminster, he adds.

Earlier this year, SNP leader Nicola Sturgeon said the party would vote on English health matters if it helped to protect the Scottish NHS.

Mr Swinney adds that the SNP's top priority is to use its "strength " in Westminster after the general election to end austerity, which has done "enormous harm" to Scotland.

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The Today programme’s latest piece in its 100 seats series comes from Aberconwy. Reporter Hywel Griffith spoke to retired voters about their concerns and considered whether the so-called “grey vote” still exists. One of those he met, Jacqueline Millband-Codman, raised the issue of the EU, asking: “Why are they so intent on keeping us in? Why can’t we go it alone like we used to?” Listen again here.

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Today will see Labour launch a week of intensive election campaigning on the NHS, with speeches due from leader Ed Miliband, shadow chancellor Ed Balls and shadow health secretary Andy Burnham. The party will declare that the health service is on "life support" and claim the Conservatives will "pull the plug".

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David Cameron is to raise fresh concerns over the impact of SNP policies on the rest of the UK, in a speech later. He will promise new protections for voters in England, Wales and Northern Ireland - saying he does not want them to lose out because of decisions taken in Scotland.

The prime minister will say a Conservative government would annually review the impact of devolved policies - including tax rates, health charges and university tuition fees - across the union, with the chancellor reporting to Parliament on how he would mitigate any harm.

One example could be air passenger duty. The Scottish government has decided to cut it and Mr Cameron will say English regions could take compensatory action if their airports are adversely affected.

BBC Radio 5 Live

Ed Fieldhouse, a professor of social and political science at Manchester University, is on BBC Radio 5 Live talking about voter registration. He explains that changes to the process mean individuals now have to register to vote themselves, when it used to be done by the head of the household.

He says there was a "drop off" of about 800,000 electors - or 1.8% - between December 2013 and December 2014. But he adds that numbers are beginning to pick up again, with 1.6 million new applications to register online in the last month - in part, he says, because of a drive to boost registration.

Norman Smith
Assistant political editor

It's striking the extent to which the fear of Nicola Sturgeon has become integral to the Conservatives' election campaign. I think they rather view her as General Blucher in Waterloo. They have played the economic credibility card, the Cameron leadership card, and they have sprayed money all over the place - but none of it has provided them with a breakthrough. So they are hoping this could tilt the balance in their favour, as English voters will recoil at the idea of the Scottish tail wagging the English dog.

Norman Smith
Assistant political editor

It's the SNP's manifesto launch later, and we are expecting a bold declaration of intent from Nicola Sturgeon, who believes the SNP is poised not just to shape who will form next government but also the policies they pursue. In a Guardian interview, the SNP leader predicts some kind of post-election arrangement with Labour, and dismisses Ed Miliband's rebuff to her during last week's TV debate as "pre-election talk".

She wants to force on him a bolder, more radical agenda, including an end to austerity and reversing some benefit cuts. The SNP has also indicated it would vote on the vast majority of issues at Westminster - bar English local government - and not just devolved areas.

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