Mr Blair, Speaking at the NBAD Global Financial Markets Forum 2016 in Abu Dhabi, said Britain would be hit by a fresh wave of uncertainty should voters back the Brexit.
He said: “I’m voting to stay, obviously. We can all see what’s happened with the pound and the markets. We face a period of prolonged uncertainty, and I think Britain needs Europe and Europe needs Britain.
“But I also think we would be hit by a fresh wave of uncertainty if Britain voted to leave, since it completely alters the argument in Scotland about Scotland leaving Britain.
“I think we will vote to say in the end [because of] the common sense of the British people.
“But this is politics today, and you have to be careful of making certain predictions in what is a highly uncertain world.”
Mr Blair said that social media had changed politics – making it easier for fringe figures such as Donald Trump to “take over political parties”.
He added: “Sometimes I look at politics today and wonder if I still understand it.”