Ross Greer pledges to 'take on the super rich' as he launches Scottish Green leadership bid

Mr Greer, who was elected as an MSP at the age of 21 in 2016, said he would fight to fix a system "rigged" by the wealthiest.

He also advocated universal free bus travel in Scotland - a move he admitted would initially cost a "substantial" sum.

Mr Greer has long been seen as a potential successor to Patrick Harvie, who announced he was standing down as the Greens' co-leader earlier this year.

Under the party's rules, co-leaders serve two-year terms and one of them has to be a woman. Lorna Slater, the current co-leader with Mr Harvie, has said she will run again. She is being challenged by Gillian Mackay, the MSP for the Central Scotland region.

Mr Greer, who was raised in Bearsden, was one of the architects of the Bute House Agreement between the SNP and the Greens, which collapsed in April last year.

He said he would be "absolutely willing" to work with John Swinney's SNP after the Holyrood election next year, "if we are going to deliver policies that make Scotland a greener and a fairer place".

Greer defends record

At a leadership launch event in Glasgow, the 31-year-old defended his track record following criticism from those within the Greens who are pushing for a more radical approach.

"The only person in the history of devolution who has done more to redistribute wealth and tax the super rich than me is Patrick Harvie, and it's me and Patrick that this particular grouping seem to be criticising," Mr Greer said.

The West Scotland MSP said his party needed to "take on the super rich", adding: "It is the extremely wealthy who need to pay for the kind of transformation that we need in our society."

Asked what this might mean in practice, he said: "One of the first examples is simply ending the tax breaks that the super rich already have under devolution. There are Tory MSPs in Parliament who are some of Scotland's biggest landowners and who get tax breaks for their shooting estates - tax breaks that are designed for small businesses."

Mr Greer said Scotland's income tax system "is already by far the most progressive in the UK because of the Scottish Greens", adding: "This year alone we're raising about £1.7 billion more than we otherwise would if it wasn't for the income tax changes secured first by Patrick Harvie and then by myself as the Scottish Greens' finance spokespeople.

"There is a little bit more progress that we could make on income tax - there's always a bit more that you could raise. You can always make the system a little bit more progressive.

"But what we really need to do now in Scotland is pivot towards taxing the wealth of the extremely wealthy, particularly in relation to property. Some of the richest people in this country pay very little income tax because that's not how they arrange their finances.

"That's why we need to look at wealth taxation in particular, and also emissions-related taxes. We need to tax big polluters."

Free bus travel for all

Mr Greer said half of Scotland’s population can already travel on the bus for free, at a cost to the public purse of about £400 million a year.

"So if you were to make it universal for everybody, immediately, day one, that would be another £400m,” he said. "In practice it's not going to cost that, though, because part of the costs of that scheme are obviously administering it to check - are you under 22? Are you over 60? Are you disabled?

"If we make it universal, we take the admin costs out of the process. But it's also something that we would be phasing in over a couple of years.”

Mr Greer pointed to countries such as Malta and Luxembourg, which have already introduced universal free bus travel.