EU leaders would be willing to tighten up the free movement of the bloc's citizens to accommodate Britain and so the option of reversing Brexit must be kept on the table, former British prime minister Tony Blair has said.
However, former Taoiseach and ex-EU Ambassador to Washington, John Bruton, has said there are both legal and political obstacles to changing EU policies on the free movement of people.
Mr Blair claimed the Conservatives lost their majority in the British general election because large numbers of people voted to deny Prime Minister Theresa May the mandate for a so-called "hard" Brexit.
Mr Blair suggested the "will of the people" may be changing as the difficulties of Brexit negotiations become apparent and called for a "proper debate" over the different options, including remaining in a reformed EU.
The only reason it is not on the table is because the Tories fear old internal wounds would be reopened if Brexit does not happen, he said.
The former British Labour leader also criticised his party's vision of a "jobs first" Brexit outside the single market, calling it a "contradiction in terms", and said he was "dubious" about the idea that it helped win over Remain and Leave voters in the UK general election.
Pro-EU voters will eventually begin to understand Labour holds the "same damaging position" as the Tories to leaving the single market to end free movement, and the party should instead champion a "radically distinct" position on Europe, said Mr Blair.
"Rational consideration of the options would sensibly include the option of negotiating for Britain to stay within a Europe itself prepared to reform and meet us half way," he wrote in an article for his Institute for Global Change," said Mr Blair.
"The Macron victory changes the political dynamics of Europe.
"The members of the eurozone will integrate economic decision-making.
"Inevitably, therefore, Europe will comprise an inner and outer circle. Reform is now on Europe's agenda. The European leaders, certainly from my discussions, are willing to consider changes to accommodate Britain, including around freedom of movement.
"Yet this option is excluded," said Mr Blair.
Mr Bruton said free movement is guaranteed in the EU treaty - and even if that obstacle was overcome, countries whose citizens immigrate within the EU would object to a restriction of their citizens' rights.
On the chances of Britain changing its mind on Brexit, Mr Bruton said they will have to go through the negotiations process to fully realise how damaging Brexit could be.
Only when that happens they might begin to think about abandoning the process and going back to where they started, he said.
Mr Blair's article was published alongside polling which suggested 70% of Britons would support free movement if it was reformed to mean EU citizens would not have an automatic right to move to a country without a job offer, and if there were stricter controls on welfare.
German and French voters would favour similar controls, the polling suggested.
"We are all learning, as we proceed, the damage Brexit will do," Mr Blair said.
"Europe knows it will be poorer and less powerful without us.
"We know our currency is down around 12%; already jobs are going; there is not £350 million a week more for the NHS; and we actually need most of the migrants who come to work in the UK.
"On any basis, leaving is complex and will take years.
"Brexit is the biggest political decision since the Second World War.
"Given what is at stake, and what, daily, we are discovering about the costs of Brexit, how can it be right deliberately to take off the table the option of compromise between Britain and Europe so that Britain stays within a reformed Europe?"
Mr Bruton said the British are looking at the negotiations solely from the point of view of what would be good for Britain, but a successful negotiation must be good for the other side as well, and as Brexit is a British idea it is up to them to come forward with ways to make what they want acceptable to the other 27 countries.
He said he does not think London has even begun to think about that.
Mr Blair told the BBC’s Today programme: "Europe itself is now looking at its own reform programme. They will have an inner circle in the EU that will be part of the eurozone and an outer circle. They will make reforms that I think will make it much more comfortable for Britain to fit itself in that outer circle.
Mr Bruton added that from the EU side it makes sense to have a best available alternative if a deal can not be made. Such a deal would be that Britain continues as a member of the EU and it should be made clear to them that offer is still on the table if they want to rethink the direction they have taken, said Mr Bruton.