He says OBR has upgraded growth forecast for next year from 1.3% to 1.6% and expects 800,000 new jobs will be created by 2022. "The scale would be very hard to predict, given the lack of precedent".
In a move created to put the United Kingdom at the forefront of global action to adapt tax systems to the digital age, the Chancellor announced a £400 million levy aimed at internet giants such as Google and Facebook.
Both the Chancellor and Prime Minister Theresa May were forced to deny that the package - including income tax cuts for 32 million people, a funding boost for the NHS and help for high streets - was meant to pave the way to an early general election.
The PM's spokesman said: "What the Chancellor was pointing out in relation to a budget was that if economic circumstances change, he would consider economic interventions".
Labour leader Jeremy Corbyn then gets the first response, before MPs debate the Budget.
Full departmental spending allocations would be set out next year, Hammond said, but he also announced a series of funding increases brought forward to deal with services pressures.
"All of the spending commitments that the Chancellor will set out today are funded irrespective of a deal", said the PM's spokesman.
"Mr Hammond said it would put "£130 in the pocket of a typical basic rate taxpayer".
Heidi Allen expressed her worry that the Chancellor's promise of billions to address concerns about the rollout of the flagship welfare reform would "only fix the symptoms", rather than the cause.More news: "Can't Believe It": Pak Christian Woman On Acquittal In Blasphemy Case
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Mr Johnson said there would be "millions of losers" from the introduction of Universal Credit, despite an injection of around £2bn per year to ease the transition to the controversial new benefit.
"Unless the United Kingdom leaves the European Union in March 2019 without a deal, there must be a good chance that economic growth will turn out better than the OBR's forecasts suggest - the Chancellor's so-called "double deal dividend", says Ruth Gregory, an economist at Capital Economics.
"The Chancellor has made clear that this budget will need urgent attention in the event of "no deal", showing yet again the seriousness of the situation and the need to get a good deal over the line".
We are confident that we will secure a deal which delivers that dividend.
But Dame Margaret Hodge, a former chairwoman of the Commons Public Accounts Committee who repeatedly challenged tech giants over their taxes, said the £400 million tax was "simply gesture politics". Total borrowing would fall every year and reaching £19.8bn in 2023-24.
It is thought he will announce extra cash for roads - with a £28.8 billion five-year programme of investment in major routes - broadband, social care and the armed forces, as well as help for small retailers.
Counter terrorism policing will receive a £160m boost to counter-terrorism police funding, and Hammond confirmed that £2bn of the £20bn-a-year boost to the NHS, announced in June, would go to beefing up mental health services. Education professionals were critical both of the amount pledged - which breaks down to £10,000 per primary school and £50,000 per secondary school, less than one per cent of the average school's annual budget - and the phrase "little extras", which was viewed as patronising and tone deaf.
Mr Hammond said the era of austerity was finally coming to an end as he delivered his last Budget before Brexit.