The arch-Remainer said the decision to leave the EU would torpedo Britain’s remaining global clout and be regretted for generations to come.
Mr Blair, Labour prime minister from 1997 to 2007, said Britain would be poorer and weaker, and he warned Theresa May had solved none of the problems over Northern Ireland’s post-Brexit status.
The 64-year-old wrote on his website: “2018 will be the last chance to secure a say on whether the new relationship proposed with Europe is better than the existing one.”
And in an interview on Radio 4 he told John Humphrys Britain needed a second referendum because people “didn’t know what the terms of the new relationship will be”.
Mr Blair’s comments have sparked fury on social media with people blasting the former Labour leader and telling him to respect the will of the people.
Former Ukip leader Nigel Farage led the attacks, with a simple tweet highlighting Mr Blair’s past record on speculation.
The MEP wrote: “Wrong on the ERM. Wrong on the Euro. Wrong on Brexit!”
TV host Piers Morgan backed up Mr Farage’s comments, saying: “I remember Tony Blair telling me that if Britain didn’t enter the Euro, it would lead to financial disaster for the country.
“Then he told me Britain had to go to war with Iraq because Saddam had WMD. So I’d take his ‘Brexit will be a disaster’ claims with a pinch of salt.”
Chair of Labour Leave, John Mills tweeted: “I have always taken arguments to task, rather than individuals.
“But Tony Blair’s repeated efforts to frustrate the will of the British people are wrongheaded, undemocratic, and could leave us with a very bad deal indeed.”
The official Leave EU twitter account hit out at Mr Blair too, writing: “Tony Blair piping up again trying to stop us from leaving a political institution he himself campaigned against and admitted in 1983 had ‘drained our natural resources and destroyed jobs’.”
UKIP MEP Patrick O’Flynn accused Mr Blair of simply wanting an EU superstate.
He wrote: “More and more people seem to be realising the real extremists about Brexit are those, like Mr Blair, who would block the will of the people in pursuit of a barmy EU superstate.”
Many other social media users were infuriated at the thought of another referendum.
One user, Chloe Gobell, savaged Remoaner Mr Blair writing: “Why does Tony Blair think he’s still relevant ??”
The ex-PM has repeatedly called for a Brexit reversal, echoing other critics such as French President Emmanuel Macron and billionaire investor George Soros, who have suggested Britain could still change its mind.
But so far, opinion polls show little sign of a change of heart among voters on Brexit and it is unclear how it could be stopped if both major political parties support the divorce.
Supporters of Brexit accused Mr Blair of undermining both Britain’s negotiations with the EU and the will of the people.
Richard Rice who helped found one of the two Leave campaign groups told Reuters: “Blair and his elitist gang are damaging our negotiating strength, thus damaging our national interest by their continuing efforts to undermine democracy.
“History will not forgive them.”