British chancellor George Osborne today slashed the official growth forecast in half as he admitted economic recovery was taking "longer than anyone hoped".

In his budget speech, which began shortly after 12.30pm, he said the economy would grow by just 0.6 per cent this year — down from the previous forecast of 1.2 per cent — and would be slower than forecast next year at 1.8 per cent compared to the 2 per cent forecast at the time of the Autumn Statement.

Declaring "Britain is open for business", Mr Osborne announced a series of measures designed to boost commerce, including a 1 per cent cut in corporation tax to 20 per cent in April 2015.

And he confirmed more measures aimed at curbing tax dodging, claiming it was "one of the largest ever packages of tax avoidance and evasion measures presented at a budget".

He described today’s package as a “budget for people who aspire to work hard and get on”.

But he added: “Today, I’m going to level with people about the difficult economic circumstances we still face and the hard decisions required to deal with them.”

Mr Osborne delivered his budget to a rowdy House of Commons in which the deputy speaker was forced to intervene repeatedly.

He said a planned 3p rise in beer duty tax was being scrapped and replaced by a 1p cut on a pint of beer.

And he brought forward a rise in the personal allowance to 2014, meaning no income tax is paid by anyone on the first £10,000 of their earnings.

He also announced a new employment allowance which will take the first £2,000 off employer National Insurance bills for every company in the country - a move he described as "taking tax off jobs".

On energy, the chancellor announced a boost for the controversial shale gas industry, which collects gas using a process known as fracking.

Mr Osborne said the "generous new tax regime" would include a shale gas field allowance.

He said: "Shale gas is part of the future. And we will make it happen."

Meanwhile, the political editor of the Evening Standard apologised after details of the budget were published on Twitter before the chancellor delivered his speech to MPs.

While Mr Osborne was on his feet delivering the budget, the Labour front bench were closely studying photocopies of the Standard splash which had been tweeted.

Joe Murphy tweeted during the speech: "I wish to apologise for a very serious mistake by the Evening Standard earlier which resulted in our front page being tweeted.

"We are so sorry to the House of Commons, to the Speaker and to the Chancellor for what happened. We shall be apologising to them."

In 1947, Labour chancellor Hugh Dalton had to quit after a Budget was leaked before it was delivered in the Chamber.

This morning, Labour leader Ed Miliband said it was time for the chancellor to admit that a “change of course” is needed to inject growth into the economy.

"What I want to hear from the chancellor today is a willingness to change course, not more of the same," said Mr Miliband. "His economic plan is failing. It's failing Britain's businesses and Britain's families."

Families are seeing their living standards fall year-on-year, while the chancellor has given a tax break to the rich which comes into effect in less than a fortnight, said the Labour leader.

“The Government is borrowing over £200 billion more than he had planned,” added Mr Miliband. “Why? Because it’s paying for failure. Its failure to get growth moving. And it’s also making Britain’s families pay for that failure.”

More to follow...