Jeremy Corbyn has once again defied the expectations of opponents and pollsters with a Labour result that may not necessarily put him in Downing Street, but has delivered a hung parliament rather than the anticipated cull of his MPs.

The man who began his campaign to be Labour leader as a 100-1 outsider [1], and was routinely derided as unelectable [2], ended up increasing the number of Labour seats, a prospect seen by many as unthinkable when the election was called on 18 April.

As a series of Conservative target seats stayed resolutely in Labour hands, followed by a string of gains for his party, pre-election speculation about what scale of losses would necessitate a Corbyn exit was replaced by exultant talk of a new style of politics.

From the moment the exit poll arrived at 10pm on Thursday, indicating that Labour would increase its number of seats by 34, with a net loss of 17 for the Conservatives, the former was ebullient, with a spokesman saying this would be “an extraordinary result”.

“There’s never been such a turnaround in a course of a campaign,” he said. “It looks like the Tories have been punished for taking the British people for granted.”

Speaking after he held his Islington North seat with an overwhelming majority, Corbyn said he was “very proud of the results that are coming in all over the country tonight”.

He said: “You know what? Politics has changed. Politics isn’t going back into the box where it was before. What’s happened is, people have said they’ve had quite enough of austerity politics, they’ve had quite enough of cuts in public expenditure, under-funding our health service, under-funding our schools, our education service, and not giving our young people the chance they deserve in our society.”

The shadow chancellor, John McDonnell, was swift to give credit to Corbyn’s style and approach in getting across to voters, amid decidedly mixed opinion polls [3] and an often thunderously hostile media [4].

“We tried to have an extremely positive campaign,” he told the BBC. “We modelled it around Jeremy’s character. If you remember when he stood for the leadership, his slogan at the time was honest politics, straight talking, and that’s what we tried to do – a positive campaign throughout.

“And if it is reflected in this sort of levels of support, I think it does change the nature of political discourse to a large extent in our country now. I think people have got fed up with the yah-boo politics and some of the nasty tactics that have gone on recently. I think it will improve politics in this country overall.”

As the first results came in from the north-east of England, with a few showing seemingly better results for the Conservatives than the exit poll suggested, Labour candidates were split.

One candidate contesting a marginal Midlands seat was sceptical. “I don’t believe it. This does not take account of postal votes. There is no way we have gained 34 seats,” they said.

However, one Labour MP in a safe seat said turnout had soared in their constituency. “People who never vote [are] coming out. If replicated, [it] means YouGov right,” they said. “Just depends if nationally it translates to local, or if vote has racked up in areas like this at expense of others.”

But as more results came in, showing Labour holding on to a series of seats the Conservatives had banked on winning, such as Darlington and Wrexham – the latter was where Theresa May reversed her manifesto plan for social care [5] – the mood picked up.

Then came a series of Labour gains, evicting the junior Treasury minister Jane Ellison in Battersea – London was looking especially strong for the party – and beating the Liberal Democrat Greg Mulholland in Leeds North West.

There followed more unexpected gains still – taking Nick Clegg’s Sheffield Hallam seat and prising Cardiff North from the Conservatives. The party even narrowly took Canterbury, a seat that had been in Tory hands since the mid-19^th century.

One re-elected Labour MP who had previously opposed Corbyn, said it was vital for the party to unite, especially if it was narrowly unable to form a government. “A lot of people were saying they were frightened of the future and wanted an alternative,” he said.

“I think we all have a responsibility in the Labour movement now. Those people will not want us to step back. They will want us to be more than an opposition – they will want us to be an alternative.”

Tom Watson, Labour’s deputy leader, who comfortably retook his West Bromwich East seat, a constituency the Conservatives had held some hope of taking, also hailed the positive tone of Labour’s campaign.

“The next few hours, maybe the next few days, look very uncertain,” Watson said in his victory speech. “But one thing we can be sure of is that Theresa May’s authority has evaporated. She is a damaged prime minister whose reputation may never recover.

“One thing is for certain: people want hope. And when they’re offered it, they vote for it.”

Labour seemed to have benefited from a swing of opinion in Wales, taking back Vale of Clwyd from the Conservatives, with other constituencies also predicted to return.

The former Welsh secretary Peter Hain, who was not a notable supporter of Corbyn, described it as “a good night for Welsh Labour and a bad night for the Tories”. On the Labour leader, Hain said: “To his great credit, he has energised his party.”

Even with many more results yet to come in, it was clear that the much better than expected Labour result had quashed any talk of another internal challenge to Corbyn, less than a year after 172 of his MPs passed a vote of no confidence against him [6].

May called the election in no small part because polls indicated that not only was Labour lagging badly, but people’s personal opinion of Corbyn was deeply unfavourable.

The seven-week campaign saw the Labour leader take on these unfavourable indicators and much of the media with a campaign the party sought to portray as positive and forward looking, in contrast to May’s safety-first approach.

It was not without challenges, including a series of leaks before Labour’s manifesto was launched [7] and some uncomfortable interviews, in which Corbyn forgot the budget for his childcare policy [8], and Diane Abbott, the shadow home secretary, confused over the cost of extra police [9].

The day before the election, the party also had to deal with Abbott’s temporary departure from her role after it emerged that she had a long-term health problem [10].

But the gap narrowed, albeit within a wider context of sometimes very varied poll numbers. Corbyn’s personal approval rating rose while that of May fell [11].

Separate polling showed considerable support for many of the policies in Labour’s manifesto [12], including more tax on higher earners and nationalisation of the railways [13].

Some focus groups found that voters appreciated Corbyn’s apparent openness, in contrast to more than May’s relatively safe and sterile approach, which saw her rarely deviate from a limited palette of approved catchphrases [14].

Peter Walker and Jessica Elgot