Lord Scriven of Sheffield also claimed that Sir Gary and the tourism body's former chairman, Ron McMillan, competed to order the most costly wine on expenses, while shooting expeditions at £2,500 a day were enjoyed as "networking" opportunities.
Speaking in a House of Lords debate, the former Sheffield Council leader called for an overhaul of the Freedom of Information Act, so that the culture of bodies like Welcome to Yorkshire, which receive public funding, are open to proper scrutiny.
Lord Scriven said "major excesses and scandals" at the tourism organisation, dating back as far as 2012, had not been exposed because Welcome to Yorkshire is a private limited company.
Some of those excesses would not have happened and some of the people responsible for them would have been relieved of their duties earlier if the body was subject to Freedom of Information Act rules, he said.
However, under current limitations of the rules, a private body is "totally out of scope" of Freedom of Information legislation, even it is receives taxpayers' money, he said.
Welcome to Yorkshire has been handed more than £10m from local authorities across the region over the last 10 years.
'Ends have to justify the means'
"Due to the lack of freedom of information, no one really knows what has been going on under the auspices of Welcome to Yorkshire," said Lord Scriven, who praised The Yorkshire Post's Chris Burn, among others, for helping to expose the "toxic culture" that had been going on at the body for "many years".
He continued, saying: "Many have said it has been a successful organisation in bringing the Tour de France and the Tour de Yorkshire there. However, the ends have to justify the means - and the means are quite breathtaking.
"There have been major excesses and scandals that nobody has been able to get to for years and years, starting back in 2012, because every time we asked for information we were told it was a private company and nothing to do with us."
He said it was unknown how much money had been paid out by Welcome to Yorkshire on non-disclosure agreements with former staff following bullying accusations, with Sir Gary having had 20 personal assistants in the last 11 years.
'Excesses demonstrate need for extended Freedom of Information powers'
Going on to detail alleged "excesses", Lord Scriven cited luxury spending on helicopters; hotels at £600 a night; lavish meals during which Sir Gary and Mr McMillan played games involving who could get the most expensive wine on expenses; chauffeur-driven cars to take people a few miles; pricey "networking" shooting expeditions, and expeditions around the country.
"Only yesterday it came to my attention via a former employee that there is a possibility that a flat in Leeds, which was either purchased or had its mortgage or rent payments paid, was given to Gary Verity for him to stay there, and that that flat is now rented out and the former chief executive claimed hotel expenses while in Leeds," Lord Scriven said.
"This is why freedom of information is important. Only yesterday I asked the interim chair, Keith Stewart, to clarify this and got an email refusing to do so, saying that it had given me the courtesy of answering one question about expenses yesterday and was going to answer no more.
"Serious allegations are made about the misuse of public money, and nobody can get to them. That board has closed ranks and is not giving taxpayers the views they need."
Tourism body responds
Mr Stewart, interim chairman of Welcome to Yorkshire, said: "I understand Lord Scriven’s frustrations with the past failings of the organisation which is why we instigated two independent investigations. They have now concluded and the reports, which Lord Scriven rightly points out are damning, have been made available to the public.
"We agree with all of the findings in the reports- what happened in the past is unacceptable and I apologise on behalf of the board for those failings in governance and leadership at the highest level. Where we have let people down we are truly sorry."
Mr Stewart added: "Myself and the board fully accept the recommendations in the two reports and are working hard to implement all of them, including a commitment to far greater levels of transparency in future.
"Welcome to Yorkshire has achieved great things over the last 10 years, raising the profile of this county to new global heights through major international events, helping to increase the visitor economy to £9bn a year, and in doing so helping to create and sustain jobs.
"We look forward to continuing to build on those achievements with the help of everyone in the tourism sector.
"We will put right what has gone wrong and we will once again become an organisation that everyone can be proud of."