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Shadow employment minister Stephen Timms says the Tory proposal is "a pretty implausible and panicky gimmick". He says "the numbers don't add up" and suggests that the Tories could put VAT up and then pass the law, rendering it somewhat meaningless.

On Labour's plans to increase the top rate of income tax to 50p, Mr Timms won't be more specific than predicting that it will "bring in a very worthwhile sum". He admits that "I don't know the figure". The Institute for Fiscal Studies, Mr Timms is helpfully informed, thinks it will only bring in £110m. That's a "useful" and "worthwhile sum", Mr Timms says.

Daily Politics
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In extreme circumstances, William Hague concedes, the government could reverse the Conservatives' tax lock. But "it will be far more difficult once legislation is passed", he insists. "It does underline the commitment we've made... it's planning ahead and giving people confidence to plan ahead."

The question then becomes: why won't tax credits, child benefit and other unprotected taxes be protected? Working age benefits are to be frozen, Mr Hague says. On working-age child benefits, he says that's included too.

Asked why the policy wasn't included in the manifesto, he offers a very campaign-focused answer: "It's important to have things announced after the manifesto."

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What percentage of total tax revenues does the "tax lock" cover, William Hague is asked as he appears on the Daily Politics. "The great majority," he replies, before being told the answer is 67%. "There you are," Mr Hague says. What happens if taxes do need to be increased, though? The ex-foreign secretary replies by saying that Britain is in a much stronger position than five years ago. "We are in a completely different financial position in this country so we are able to make these commitments," he says.

When George Osborne's quote about Alistair Darling is put to him (see 11.17), Mr Hague says the chancellor of the time "intended to legislate for the opposite of what he had actually done". This, by contrast, is about doing something "we've committed to doing anyway".

Daily Politics
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BBC political editor Nick Robinson and Deborah Mattinson pick over Ed Miliband’s prospects amid deadlocked national polls. Was going to see Russell Brand a good idea? Leveraging the young vote might be worth a go, Ms Mattinson thinks. “The interesting question is whether you see it or whether you read or hear about it,” Mr Robinson says. When people see Mr Miliband, he suggests, they will often be impressed. But the “largely Tory media coverage” questioning the point of the interview could lead others to conclude he’s not being statesmanlike.

Darren Glasper:

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Political strategist Deborah Mattinson tells the Daily Politics that Nicola Sturgeon “can do no wrong” at the moment, as the programme considers this morning’s Ipsos Mori poll. But our political editor, Nick Robinson, says he’s being controversial as he suggests she’s not often asked tough questions. “Do you remember Peter Snow used to say ‘just a bit of fun’ [about opinion polls] – I don’t recommend you putting your money on winning every seat in Scotland.” The pair agree on the idea of ‘shy’ Scottish voters – those who aren’t prepared to say they’ll vote for a party they don’t think is considered to be "cool".

This morning’s air pollution ruling has been seized on by the Greens. The Supreme Court, if you hadn’t spotted the story just yet, ruled that the government must take immediate action to tackle unacceptably high nitrogen dioxide levels in the air.

“It is scandalous,” says the Greens’ local transport spokesperson Caroline Russell, that the government has “delayed so long knowing the very serious public health impact of their failure to act”.

Image source, PA

Defra, which says it has already started revising its plans to meet EU targets, now has seven months to come up with a plan for reducing emissions.

Liberal Democrat Energy and Climate Change Secretary Ed Davey has also has his say, too, putting a party-political spin on the issue:

The Conservatives said on Sunday that they’d spend the week focusing the economy, and so they have; today, just outside Birmingham, David Cameron said there were big choices ahead on the deficit, tax and welfare; who do you trust, he asked, on each of those?

He was asked about the promise of a five-year tax lock – a law that would restrain any government from making any increase in income tax, VAT, or national insurance over the next five years; why now? And why did the Conservatives raise taxes when they came to power five years ago?

“I’ve seen the books” this time around, said Mr Cameron, and that's why this commitment could be made.

Nick Clegg has been visiting a school in Chippenham this morning to launch the Lib Dems' free school meals plan, but he also found time to meet with members of "UKID" and look through their "manifesto".

Modernise classrooms - okay. More amusement - sure. New punishments? Er...

Andrew Neil
Daily and Sunday Politics

On Wednesday’s Daily Politics, Andrew Neil is joined by the political strategist Deborah Mattinson to look at the polls, and will debate Conservative and Labour tax plans with William Hague and Stephen Timms. Today's smaller party focus is on Animal Count, and there will be a look back to the 1992 election to see if there are any parallels with the current campaign.

Meanwhile, BBC political editor Nick Robinson makes his first Daily Politics appearance of the election campaign in the first edition from 12:00 BST.

Andrew will be back for a health debate on BBC2 England with Conservative Jeremy Hunt, Labour’s Andy Burnham, Lib Dem Norman Lamb, the Green Party's Jillian Creasy and UKIP’s Angus Dalgleish at 14:00 BST. Viewers in Scotland and Wales will see separate programmes.

Image source, ITV

Ed Miliband is then asked about the plight of carers by Rebecca. "I can't promise you we'll increase the carers allowance," he tells her. "I'm incredibly sympathetic but because we've got to get the deficit down and I'm not going to make promises I can't keep." But Mr Miliband says the NHS has to get better at identifying carers and giving them support, and the local authority budget for respite care should be protected.

Another scathing George Osborne quote about Labour's plans to enshrine tax and spend targets into law. A nod to our colleague Gavin Stamp for this one the chancellor fired at his Labour predecessor Alistair Darling...