The potential consequences of Scottish independence were underlined when David Cameron was told that the UK parliament would need to be overhauled if Scotland broke away from the union.

The first minister of Wales warned that radical changes would have to be made to prevent England dominating a new United Kingdom.

Carwyn Jones spoke out at a meeting of the British-Irish Council in Dublin after Alex Salmond appeared to draw a parallel between London's treatment of Scotland and its historic behaviour towards Ireland. The first minister then softened his rhetoric to invite the prime minister and Nick Clegg to Scotland to discuss their plans to accelerate a referendum on Scottish independence.

British sources, who pointed out that Salmond had declined to respond to an invitation this week to talks from the Scotland secretary, Michael Moore, were scathing about the first minister. "Alex Salmond has a friendly chat with Nick Clegg over a cup of coffee in Dublin and they agree to keep talking as they always do. Then his people go and brief that a formal invitation has been issued. Alex Salmond is a bandit," said one source.

Peter Robinson, the Democratic Unionist first minister of Northern Ireland, launched an impassioned plea for Scotland to remain in the UK.

And the scale of the political forces unleashed this week was further highlighted when the first minister of Wales said that a convention would have to be held if Scotland left the UK. Jones said: "You can't just take Scotland out and expect the United Kingdom to continue as before. You would have, for example, parliament in London with about 550 MPs, 510 of whom would be from England.

"There would need to be a fundamental rethink of the nature of the relationship between the three nations left within the UK to ensure that what is then the UK is a stable body where people think they have fair representation."

Jones later told the Guardian that a convention should look at following the example of the US. The House of Commons would be balanced by a new upper house that would ensure Wales and Northern Ireland would be strongly represented. "Why not have an upper house with equal representation from England, Wales and Northern Ireland – same as the Senate," he said. "It would be more of a federal structure. It is up to the people of Scotland what they do but it is certainly not the case that somehow things would carry on as normal."

The Welsh first minister said that the departure of Scotland from the United Kingdom would mean more than a loss of 5 million people from the UK. "We would very much regret seeing Scotland leave the union. We very much value Scotland's membership of it. We think Scotland's membership adds more balance to the UK. But if Scotland were to leave there would need to be a convention looking at the nature of the UK with England, Wales and Northern Ireland as members."

The warning followed Salmond's strong attack on the UK government after the prime minister moved to call his bluff by announcing this week that London would devolve powers to Scotland to hold a referendum on independence.

Two strings would be attached: there would be a deadline and the referendum would simply ask voters whether to remain in the UK or leave. Salmond, who fears he cannot win a straight independence referendum, would like to ask another question on whether Scotland should have greater devolution that falls short of full independence.

Salmond, who will publish his plans on the referendum in the next two weeks, gave vent to his frustration on RTÉ this morning. "I am sure many people in Ireland will remember that sometimes people who are in leadership positions in big countries find it very difficult not to bully small countries. What we have seen over the last week is a most extraordinary attempt to bully and intimidate Scotland by Westminster politicians.

"Sometimes Westminster politicians, and Nick Clegg is very much a Westminster politician, find it difficult to let go the strings of power and believe they are still in a position of dictating terms to Scotland. I'm afraid Nick Clegg and his colleagues David Cameron and George Osborne, who is very much in charge of this, are going to find out these days are over."

Clegg laughed off Salmond's attack. "I don't think Alex, if this is what he says, should be so jumpy."

Salmond was speaking shortly before the start of the British-Irish Council which is taking place at Dublin Castle, the seat of British rule in Ireland until the 26 counties of the Irish Republic achieved independence in 1922.

The castle is a mile from the general post office on O'Connell Street, the scene of the Easter Rising against British rule in 1916. It was Britain's violent response to the rising – the leaders were executed by firing squad – that helped trigger the Irish war of independence. Salmond's decision to draw a parallel between Scotland and Ireland, however obliquely, may stir a debate in Scotland, where sectarian divisions are still pronounced.

Salmond was warmly greeted by Martin McGuinness, Sinn Féin's deputy first minister, when he arrived at Dublin Castle. McGuinness later joked about the tensions between London and Edinburgh. "Peter Robinson and I have a castle in Belfast. I am sure we would be prepared to make it available for peace talks."

The announcement by Cameron that London is to seek to bring forward a referendum on Scottish independence overshadowed the British-Irish Council. It is the body established under the Good Friday agreement to promote dialogue between Britain, Ireland and the crown dependencies of the Isle of Man, Guernsey and Jersey.

Salmond was dismissive of the comments on Thursday by Osborne, who appeared to question whether an independent Scotland could keep the pound. Pointing out that Australia initially used the pound after independence, he said: "George Osborne has been chancellor for, what, 18, 20 months or so. But he seems to think he owns sterling. The Bank of England was founded by a Scot. There were Scottish bank notes before the Bank of England was founded, before the union of the parliaments."

In his strong plea for Scotland to remain in the UK, Robinson made clear that Northern Ireland unionists would lose their closest relatives in the UK if Scotland left. The Northern Ireland first minister said: "If what we have seen over the last few days is a trailer of things to come then unless we like seeing the sight of our own blood we might want to stand back somewhat. While we recognise that clearly this must be a decision for the people of Scotland to take on their own it has clear implications for the rest of the UK.

"I speak as a unionist but also as an Ulster Scot. Clearly I have a massive interest in what happens and what decision the people of Scotland will take. They do need to know that there are many people throughout the UK that feel they have a very valuable contribution to make to the UK as a whole who want to see them continue to do that."

In a reference to the Scots who travelled across the Irish Sea during the Ulster Plantation, Robinson said: "We cherish the relationship that we have. Nowhere else in the UK would the bonds be more tightly drawn between any other part of the UK from NI's point of view than with Scotland.

"Our peoples have moved from one side of that small stretch of water to the other and back again many times over the centuries. So we have a massive interest and I don't think we can sit idly by and simply indicate that it is a matter for Scotland alone. It will have implications for us all. We hope that Scotland knows just how much we want them to remain within the UK."