Sir Henry Bellingham, foreign office minister 2010 and 2012, told this newspaper that he was "extremely sceptical" of North Korea's rhetoric, but added the "catastrophic" state of the economy could convince Kim to do a deal.
The US delegation had been based at the Capella Hotel last week during talks with Mr Kim Chang Son, the de facto chief of staff for North Korea.
Refuting media reports, state department spokesperson Heather Nauert said the USA is not paying for the North Korean delegation to stay in Singapore. The Trump administration is in the midst of a peace process it hopes will end with North Korea abandoning its nuclear program.
Singapore suspended trade relations with the reclusive Northeast Asian state past year following tightened United Nations sanctions over its weapons programme, however, North Korea still operates a small embassy in the city.
Singapore also revoked all work permits held by North Korean citizens in March.
Trump announced the historic summit was back on track last Friday after an hour-long meeting with the top North Korean official.
"We have had teams negotiating not only in the Demilitarised Zone every day. meetings are taking place in Singapore as well".
This file photo shows Joseph Yun, former US special representative for North Korea policy.
North Korean officials in Singapore also needed to get sign-off on nearly every detail with their superiors in Pyongyang, leading to one- or two-day intervals before they could reach an agreement on even minor logistical details, the source said.
With just one week to go to the summit, hosted by Singapore, very few details have been publicly confirmed.
The red-shingled, colonial-style Capella is a five-star hotel on Sentosa Island, which boasts several resorts, hotels, two golf courses and a theme park.
"We said, 'Well, we're not going to have a summit under those circumstances, '" he said. "We're not paying for their expenses". "I think that's something people should be very aware of". And as the president stated, we have sanctions on.