Sir Alex Ferguson has taken a dig at "noisy neighbours" Manchester City by comparing them to the wealthily backed Sunderland side of the 1950s, who wound up being relegated. The Manchester United manager, talking in an exclusive interview to relaunch this morning's Observer, referenced Sunderland's post-war nickname of 'the Bank of England club' – and the fact that they lost their top-flight place in 1958.

Asked about the impact of City's purchase by the Abu Dhabi United Group, Ferguson said: "It has increased that competitive element between the fans and the media, no doubt about it. The decibel level went up in the last two games [the Carling Cup semi-final ties last month]. We have to get used to it, have to do something about it and accept the challenge. There's nothing wrong with having a challenge. We have to do what we're good at and hope it's good enough."

The Scot added: "[Manchester City] is a club with so much wealth they could buy every player in the world, but can they buy a team, can they buy a Manchester United spirit? I don't expect City to be bigger than us, I really don't, even with all that money. The problem with having all that money is that you buy indiscriminately. Sunderland, in the 1950s, the Bank of England team – relegated. I wouldn't wish ­relegation on City."

Ferguson also addressed his own club's ownership, saying that while he understood supporters' concerns and respected their right to hold forth on the state of the club under the Glazer family, he had always found the American owners supportive. "I'm never against protest," he said. "I've been brought up in protest all my life. I was involved in the [Govan shipyards] apprentices' strike of 1961 ... It's everyone's right, there's no doubt about that."

But he added: "My problem with it, being manager of Manchester United, is that I've got owners who have never caused me any bother. Any time I've asked for money they've given it to us ... The debt has concerned a lot of people. David Gill [the club's chief executive] has had a lot of chats with the staff to settle them down, to assure them everything's fine. As far as I'm concerned, I bought [Chris] Smalling for big money [£10m for the Fulham centre-back]. So for me, life goes on. As I say, the Glazers have been fine with me, I've never had any problem."