When asked, ‘Why don’t you like U2′, he said, “Because they wear cowboy boots.’

“Any songwriter knows that they have to write about things that they care about,” agrees The Edge.

“That’s when it connects and when it means something. Otherwise, it’s artifice.”

Throughout the Ivors ceremony, U2’s decades-long friendship is apparent – albeit through relentless, good-natured taunting.

They try to goad The Edge into dancing for the BBC’s TV crew. Mullen reminds his bandmates of their 1990s penchant for cross-dressing. Bono dredges up Paul Weller’s scathing critique of their band.

“When asked, ‘Why don’t you like U2′, he said, “Because they wear cowboy boots.’

“‘I rest my case.'”

Thankfully, the cowboy boot era is ancient history (tonight Bono wears Cuban heels) and, Weller’s opprobrium aside, U2 became one of rock’s biggest bands, selling more than 175 milllion albums worldwide.

There were missteps along the way – Clayton famously disappeared on a drinking bender during the New Zealand leg of the colossal two-year Zoo TV tour (he’s now sober and appearing on Gardener’s World), while the band have repeatedly apologised for the misguided decision to pre-load their 2014 album, Songs of Innocence, on to people’s iPhones.

“The free U2 album is overpriced,” wrote one disgruntled user.

In his autobiography, Bono said he took “full responsibility” for the stunt.

“I’d thought if we could just put our music within reach of people, they might choose to reach out toward it,” he wrote.

“Not quite.”

But as they enter their fifth decade, the band are ready to “re-apply for the job of best band in the world”, as they memorably put it in 2001.

A year ago, Bono expressed his desire to release “a noisy, uncompromising, unreasonable guitar album”, citing AC/DC as an influence.

At the Ivors, I accidentally misquote this back to him as “an unassailable guitar record”.

“I’m really pleased with that adjective – unassailable,” he says, trying it on for size.

“I think he said, ‘un-sellable’,” shoots back Mullen Jr.

“But listen,” says Bono. “We have a guitar genius in our band, and the only person who doesn’t know it is him.

“We tell him every day, but he insists on playing the piano… and sometimes the spoons.”

“It’s blackmail,” insists The Edge, the famously unflappable guitarist seeming temporarily flapped.

“The fellas are all on about this guitar album we’re making, and I’m at home, going, ‘Okay, I’d better get on with it'”

The clock is ticking…