The 43-page document for the June 8 election was due to have an official launch next week but the version that emerged late Wednesday outlines sweeping reforms.
The 43-page document for the June 8 election was due to have an official launch next week but the version that emerged late Wednesday outlines sweeping reforms including renationalisation of railways and some tax rises.
Among the pledges, which are yet to be signed off, the party said it would guarantee a "meaningful vote" on the final Brexit agreement and rules out leaving the European Union without a deal.
"Labour recognises that leaving the EU with 'no deal' is the worst possible deal for Britain and would do damage to our economy and trade.
"We will reject 'no deal' as a viable and negotiate transitional arrangements to avoid a cliff-edge for the UK economy," the draft manifesto said, according to The Daily Telegraph newspaper.
Labour is lagging behind in the polls, with strong suggestions that leader Jeremy Corbyn's lack of a clear line on Brexit is to blame.
Corbyn on Tuesday refused five times to answer directly when asked by the BBC if Britain would leave the EU if he was prime minister, although a party source later told AFP there was no question Brexit would happen.
The draft manifesto also details Labour's view on immigration -- a key factor in Britain's referendum last year on leaving the EU.
Labour pledges to make no "false promises" on cutting the number of migrants, in a nod to the Conservatives' unfulfilled promise to reduce arrivals to tens of thousands.
As well as renationalising railways, the party of veteran socialist Corbyn also plans to introduce state-owned energy firms and hike corporation tax on large companies, said the media reports.
The reshaping of public finances will also include borrowing £250 billion ($323 billion, 297 billion euros).
Gains from a rise in income tax for those earning above £80,000 will be used to invest £6 billion in Britain's treasured National Health Service, The Daily Mirror reported.
Other policies outlined in the draft include the scrapping of university tuition fees, which currently run up to £9,250 annually, and launching a review to slow the number of pubs closing.
A spokesman for Corbyn said the party would not comment on the leaked manifesto, which has to be approved by around 80 Labour figures before being formally published.