More than 100 senior executives from leading UK companies have signed an open letter warning any "change in course" after May 7 would threaten jobs and put the economic recovery at risk.

The letter was released as it emerged Ed Miliband is to promise legislation in a Labour government's first Queen's Speech guaranteeing employees the right to a regular contract after 12 weeks of working regular hours in practice with an employer.

The commitment - to be included in the party's election manifesto - significantly strengthens its previous policy entitling workers to a regular contract after 12 months.

In their letter sent to The Daily Telegraph, the executives - who come from some the country's best known companies - praised the Government's economic policies, which they said had supported investment and jobs.

Meanwhile, the Liberal Democrats have set out plans that would entitle new fathers to six weeks of paternity leave - three times the current amount.

Lib Dem leader Nick Clegg has also criticised his coalition colleagues, who he says have abandoned their commitment to the environment.

In Scotland, SNP First Minister Nicola Sturgeon, Labour leader Jim Murphy, the Conservatives' Ruth Davidson and Willie Rennie, the Scottish Liberal Democrat leader, will all address the Scottish Police Federation gathering in Ayrshire and take part in a question and answer session.

Events today include: Conservatives London campaign launch with Boris Johnson from 9.30am, Ed Balls and Jim Murphy in Glasgow from 1pm, Nick Clegg and Jo Swinson in East Dunbartonshire from 1.30pm and Bez from the Happy Mondays, standing for Parliament on an anti-fracking ticket, to start a second, week-long "bed-in" protest in Witney, Oxfordshire, from 2pm.

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David Cameron has tweeted about the open letter, published in The Daily Telegraph.

He tweets: "Today's business letter in the Telegraph shows job creators support our long-term economic plan. Labour's taxes will cost jobs."

New fathers will be entitled to six weeks of paternity leave - three times the current amount - under Liberal Democrat plans.

Nick Clegg will highlight the policy alongside equalities minister Jo Swinson as the Liberal Democrat leader's election tour visits Scotland for the first time.

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Fathers are currently entitled to two weeks of paternity leave, but the Lib Dem manifesto will commit to extending that period by four weeks.

The party tweets: "If we want more equality in the workplace, we need to help dads play a role domestically."

Ms Swinson said: "Shared parental leave is my proudest achievement as a minister and I'm delighted that it finally becomes a reality this week."

She added: "Today I'm calling for a dad revolution. Liberal Democrats want to triple paternity leave, to encourage new dads to spend more time with their child in those vital early weeks and months after birth.

"Most fathers want to spend more time with their new baby - and we know it makes a positive difference for children when they do."

Scotland's First Minister and SNP leader Nicola Sturgeon, Labour leader Jim Murphy, the Conservatives' Ruth Davidson and Willie Rennie, the Scottish Liberal Democrat leader, will all address the Scottish Police Federation gathering in Ayrshire today and take part in a question and answer session.

The event comes on a day when Lib Dem leader Nick Clegg and UK shadow chancellor Ed Balls will also hit the campaign trail in Scotland.