Marcus and Gary in 2011
In May, it was revealed that Gary, Mark Owen and Howard Donald could face huge bills after paying into the Icebreaker Management Partnership scheme.
Gary faced a huge amount of criticism when the news became public and some critics - including Ed Miliband - suggested his OBE should be taken away. He was also the victim a vicious Twitter hack.
Speaking to Digital Spy, Marcus revealed he still counts Gary as a “good friend” and slammed his critics.
"I notice it more with Gary than anyone else, that as soon as something comes up where people feel they can discredit him, they come down on him like a ton of bricks," Marcus said. "I don't know why people are so quick to wish people to fail. It's such an ugly trait.
Gary isn’t the only celebrity to come under fire for alleged tax avoidance in recent months.
In July, celebrities including David Beckham and members of the Arctic Monkeys were on a list of people who had invested in the company Ingenious Media.
Ingenious denied that their partnerships are tax avoidance schemes, insisting that they are real businesses and pointing out that over £1 billion of taxable income has been generated.
However, they are also thought to have warned their investors that they may face bills from HM Revenue & Customs in the very near future.