David Greig, one of the UK's leading playwrights, has predicted that a yes vote for Scottish independence would lead to major political reforms in England, with large cities challenging London's dominance over the remainder of the UK.

Greig, writer of the hit West End musical Charlie and the Chocolate Factory, said seeing how Scotland prospered after independence would persuade cities such as Newcastle, Manchester and Bristol to seek greater political and economic freedom of their own from Westminster.

Now campaigning for a yes vote, Greig told the Guardian he believed that a decision by Scotland to leave the UK in September's referendum would lead to fresh questions being asked about London's "astonishing" power and influence in the UK, with English regions pressing for decentralisation.

"Take off your UK goggles, the UK goggles which say you never ask questions," he said. "If we started from scratch, would we have such a highly centralised, top-down governing structure as Westminster? Compared to other countries like the United States or Germany, it's antediluvian."

Civic leaders in the north-east of England were already seeking stronger economic ties with Scotland under the Scottish National party, as a counterbalance to London, he said, suggesting Newcastle, Glasgow and Edinburgh could be closer economic partners in future.

Echoing research by political scientists, Greig, who lives in Fife, said the trend to modernise the old nation state which was taking hold in Scotland and Wales, and elsewhere in the EU, would spread to other parts of England.

"It's about renegotiating the union in creative, modern terms in the world we live in. We don't need a state built for empire any more. It's absurd. We don't need to reform the House of Lords: we need to start again," he said.

Greig, who has written plays for the Royal Shakespeare Company, the Royal Court and the Edinburgh international festival, and recently put on a play based on the Norwegian mass murderer Anders Breivik, The Events, at the Edinburgh fringe and the Young Vic, is working on new theatre projects on independence. They include a series of pieces with other playwrights, including some against independence, for the National Theatre of Scotland.

He plans to take part in a bus tour around Scotland this summer by pro-independence artists and writers, to campaign for a yes vote, reviving a pro-devolution tour led by Neal Ascherson and William McIlvanney in 1997.

Greig is also writing a mini kitchen-sink drama on Twitter, the Yes No Plays @YesNoPlays, in which a married couple – the wife a yes voter and her husband a no voter, play out the independence debate over bowls of porridge and Christmas tree decorations. The 140-character comedy may be turned into a full play.

Greig, emerging as one of the main ambassadors for the wider pro-independence movement, said he became a vocal advocate of a yes vote largely because the independence debate was promoting "fascinating" thinking about democratic reform, a new constitution, abolishing Trident, a Scottish currency, asylum policy and green energy.

There was a "ball of energy" surrounding the yes campaign, he said. "It's fizzing with thoughts, fizzing with that combination of lots of different people testing ideas against each other. What I see from the no side at the moment, partly because they're winning so they think they don't have to do anything, is a monolith which essentially says 'everything is fine'."

Greig said that the outburst in October by the comedian Russell Brand, who said he had never voted, was a symptom of wider alienation with the democratic system in England; in Scotland, political activists were able to focus their anger through the independence debate.

Brand "was trying to shake the UK establishment to say something isn't working," Greig said.

"When the City of London wields such astonishing power, it entirely dictates the terms of how we view each other as human beings. We've lost the idea that an economy exists to make sure we're happy and fed. It's as if we exist to feed the economy."

Many independence supporters wanted to renegotiate the union and reorganise the UK, to give Scotland much greater autonomy but still collaborate on significant issues like a currency or energy, he said.

"If you start flipping your thinking …. our governance is far too top down; I think that the British state is far too centralised. London is essentially an entirely different economy, an entirely different society," he said. "In principle, power should be decentralised down."

A close friend and hill-running partner of Willie Rennie, the Scottish Liberal Democrat leader, Greig said it was still possible that he would change his vote if the pro-UK parties published genuinely far-reaching and substantial plans for greater devolution and reform before the referendum.

He said David Cameron had made a "stunning" and "destructive" decision not to agree to have a second question in the referendum, about increased Scottish autonomy within the UK. Senior figures in the independence campaign disagree with Greig's analysis on this, revealing privately that the SNP leader, Alex Salmond, failed to get support from pro-devolution and civic groups for a multi-option referendum.

But Greig said the result of the failure of pro-UK parties to offer real reforms instead of independence had closed down that debate and pushed people into the independence camp.

"It's channelling all discussion of democratic reform around the independence route," he said. "At the moment, the option of federalism isn't on the table. In the event of a no vote, the Scottish people have to take it on trust that some other form of democratic reform will take place."

But Greig acknowledged he was doubtful that Scotland's 4 million voters would support independence; while a majority of people active in the arts in Scotland backed a yes vote, that was unusual.

He denied claims that well-known figures in the arts who planned to vote no were being scared off by attacks from nationalists – the comedian Susan Calman was abused on Twitter after making jokes about independence. His friends who backed the UK did not make that public because they didn't feel they needed to, he said.

Salmond's government should ensure power was not concentrated in Edinburgh, and share power with areas that wanted greater autonomy within Scotland, such as Shetland, he said. .

He warned, too, that if there were a yes vote, Scotland's first independent government would make mistakes and disappoint people who had campaigned for it – "it would be idiotic to think otherwise".

Nevertheless, the energy let loose by independence would be a creative and potentially transforming force, and might unleash new thinking going well beyond that of the SNP.