Sir David Butler must be one of the few people alive to have seen Sir Winston Churchill during a moment of self-doubt.

As a 26-year-old academic specialising in elections he was summoned to Chartwell, the country home of Britain's wartime hero, to provide advice in the lead-up to the 1951 poll.

"It was around 10:00am. He was still in bed and he suddenly lent forward and said, 'Tell me young man, do you think I am a handicap to the Conservative Party?'," Sir David said.

"I wasn't a conservative, but I did think he was the greatest man in the world, and I did think he was a handicap to the Conservative Party. People did think he was past it."

Now 92, Sir David, regarded as a worldwide pioneer of TV election night coverage, recalled the meeting of a lifetime when I caught up with him in the grounds of Nuffield College at Oxford for an interview for Lateline.

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So did he confront his hero with the cold, harsh truth?

"I weasled and said, 'I don't think you are the asset you once were, but people still love and admire you'."

Churchill went on to win the 1951 election, but retired before the next one.

Sir David went on to forge his own brilliant career in academia, journalism and television. He has covered every election in Britain since World War II and written more than 30 books.

He was the first person to use the term 'psephologist' in print and the man who popularised the 'swingometer' on television.

ABC election analyst Antony Green said he was a trailblazer when it came to election night coverage from the 1950s onwards.

"David Butler revolutionised the concept of swing, how it is relatively standard across constituencies and can be used as a predictor across the country," Green said.

"He converted election night from a tallying of constituencies declared into analysis of national trends."

'Something very puzzling going on' in UK polls

Sir David has been as confused as anyone by the opinion polls that have been darting around during the current British election campaign.

The Conservatives started the campaign around 20 points ahead, but recent polls suggest that figure is now in the single digits.

"The swing recorded by the opinion polls is greater than in any previous election," he says, "There is something very puzzling going on in the polls and somebody is going to get hurt by the results and we don't know who yet."

Sir David Butler reckons Theresa May will pip Jeremy Corbyn to the post, just. ( Reuters )

When pushed, the veteran psephologist predicts a Tory victory.

"I assume that Mrs May is going to win but not by anything like the margin that was being predicted even a week-and-a-half ago," he said.

Sir David has a great love of Australian politics, having covered many federal election campaigns from 1969 onwards.

"I did fall in love with Australia and Australian politics. There's a freshness there, an openness and willingness to talk about things," he said.

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In 1973, he founded the annual Oxford University Australian Politics Lunch.

"The only rule is you're not allowed to talk about anything, except for Australian politics. And usually I'm the only pom there."

He has also written extensively about Australian politics.

"He had a major impact in Australian political science with his book The Canberra Model," Green says.

Sir David has recently joined Twitter, where he shares his encyclopaedic knowledge of politics via the handle @SirDavidButler.

The veteran analyst is not sure where he will spend election night.

"I don't know. I've always had something specific to do on election night. I suspect I might watch it at one of my son's places or maybe I'll be invited into a studio."

He believes this will be his last British election.

"I'm certain it will be my last. I'm 92 and I shan't be around in 2022 when the next election will presumably be."

Watch Steve Cannane's story on Lateline at 9:30pm AEST on ABC News 24 and 10:30pm on ABC TV