The Australian-English phrase to apply the blowtorch to somebody’s belly, and variants, mean to test somebody’s fortitude, also to put pressure on somebody.

This phrase was coined in 1983 by Neville Wran (1926-2014), then National President of the Australian Labor Party and Premier of New South Wales, to characterise the inexperience of Nick Greiner (born 1947), who, on Tuesday 15^th March of that year, had become Leader of the New South Wales Division of the Liberal Party and Leader of the Opposition of New South Wales.

Mike Steketee and Geraldine O’Brien explained the circumstances in which the phrase was coined in an article titled He’s now in blowtorch-on-the-belly politics, published in The Sydney Morning Herald (Sydney, New South Wales) of Wednesday 16^th March 1983:

At a stage of his career when most politicians are still sitting on the backbench observing and absorbing, Greiner, as much by accident as design, finds himself Leader of the Opposition confronting Neville Wran, who has reduced the Liberal Party to a mere rump.
[…]
In his 2½ years in Parliament, Greiner has developed a reputation for analytical thinking and an ability to uncover information embarrassing to the Government. He has the intellect and the ego for the leader’s position.
The real question is whether he can project himself as a leader and has the necessary toughness. Asked recently what he thought of Greiner, Neville Wran said he obviously had ability “but he hasn’t had the blowtorch applied to his belly yet.”

The earliest occurrence that I have found of to apply the blowtorch to somebody’s belly used without reference to its origin is from A law reformer with a long-term strategy, by Richard McGregor, published in The Sydney Morning Herald (Sydney, New South Wales) of Wednesday 6^th April 1983—the Labor politician Gareth Evans (born 1944) had been appointed Attorney General of Australia on Friday 11^th March 1983:

Evans nominates the fixed-term bill, family law, including property relief, a wider freedom of information bill, and a sex discrimination bill in the civil rights area as his priorities.
But the blowtorch is being applied to Evans’s belly even before Parliament sits in May—in his first meeting with the High Court on south-west Tasmania this week. A Commonwealth win, despite the noises of many pundits, is by no means certain, and any other result will be a disaster for the Government.

The phrase has come to be used in wider contexts than party politics—as illustrated by the following three texts from The Canberra Times (Canberra, Australian Capital Territory):

1-: Of Saturday 25^th June 1988:

ANU will need more than optimism today if it is to earn first place on the ACT men’s hockey premiership ladder.
The portents look good for University […] when it meets leaders Old Canberrans on the Lyneham Supergrass surface at 5.30pm. […]
The Checks are only a point ahead of ANU […].
[…]
University may snatch a draw in this match, however Old Canberrans have more pride to make up, and coach Ross Jones will be applying a sizeable blowtorch to some Checks bellies.

2-: Of Saturday 25^th November 1989:

NSW teachers will get a 3 per cent pay rise before Christmas after their federation’s final acceptance of a government package, the Minister for Education, Terry Metherell, announced yesterday.
[…]
“It’s a long overdue outbreak of peace and wonderful news for the students, parents and community of NSW,” he said.
“I think what has happened in the meantime is the blowtorch of public opinion has been applied to their bellies and they’ve realised industrial action had alienated the community.”

3-: Of Thursday 28^th November 1991:

Australian banks had been “promiscuous” lenders in the 1980s, one result being to “drive up the price of television stations and Van Goghs”, according to the chairman of the House of Representatives inquiry into banking, Stephen Martin.
It was now time, he said, to apply “the competitive blowtorch to their bellies”.