David Cameron highlights National Insurance break
David Cameron has written to more than a million businesses and charities to urge them to check if they are entitled to a National Insurance break.
He called for them to "keep more of what you earn, grow, invest" during a speech to Conservative activists.
The first £2,000 of employers' NI bills will be cut under the new allowance.
The prime minister said his was "the party of low taxes", and hinted more cuts could come if the Conservatives won next year's general election.
"We are turning people around. Britain is coming back," he said.
He said from Sunday, "millions of people will open their pay packets to find they are paying less tax or no income tax at all".
Addressing the Conservative Spring Forum in central London, Mr Cameron also said his party had "some huge fights on the horizon".
He issued a battle cry to grass root supporters, saying the stakes were "stratospheric" for the country, and warned that failure to win next May would be damaging for the country's economic recovery.
"All of this is in the balance on the 7 May, 2015," Mr Cameron said.
"Those jobs that have been created, they can go overseas. The tax cuts, they can be reversed, the deficit it can rise up again. And most importantly the hopes and ambitions that people have for their future, the sense that Britain is once again a country moving forward, all of this can evaporate."
The prime minister said the National Insurance break for businesses, which comes into effect this weekend, was part of the Conservatives' long-term economic plan and would result in "more money in people's pockets".
He wrote letters - on 10 Downing Street headed notepaper - to businesses and charities advising them of the National Insurance contributions break, the first of which he hand-delivered to a London butcher.
It urged employers to check whether they were eligible for Employment Allowance, which provides a reduction of up to £2,000 each on National Insurance contributions for an estimated 1.25 million companies, and could be claimed by ticking a box on their payroll software.
The PM wrote: "This means £2,000 cashback on the cost of jobs that you can choose how to spend. I hope you will consider using it to take on more employees."
But Labour has claimed that, despite the new tax cuts, the average British household would be nearly £1,000 a year worse-off by next May due to overall tax and benefit changes introduced by the coalition.
Vowing to fight the opposition ahead of the general election, Mr Cameron branded Labour "a party that has learned nothing from their mistakes".
To loud applause, he told activists: "Britain is coming back. We always recover from adversity, whether it was Churchill standing up to the Nazis or Thatcher nursing the sick man of Europe back to health.
"This is the comeback country of world history, and we're doing it again, coming through a hard time and coming through stronger.
"Brilliant, brave, buccaneering, beating the odds. Great Britain is coming back and everyone here can be so proud of that."
Among the other "fights" outlined by Mr Cameron were the impending local and European elections, and the Scottish referendum.
He said neither Labour nor the Liberal Democrats would give the UK a say in Europe and that UKIP could not change a thing.
His party, he said, would fight for "Britain's national interest".
Mr Cameron also urged people in Scotland to vote against independence in September's poll.
He described the country's first minister Alex Salmond as a man without a plan.
"Once he wanted the euro, now he wants the pound," Mr Cameron said.
"Next he claims he'd be canny with Scotland's money then he splashes £2bn on spending promises without a clue about how he'd pay for them."
He likened Mr Salmond to someone wanting a divorce and asking to keep the joint bank account.
However, Scotland's Deputy First Minister Nicola Sturgeon said a currency union was in the interests of both countries "which is why it will happen".
"Only independence can allow us to use Scotland's vast wealth to build a fairer and more prosperous country," she added.