Former British Prime Minister Tony Blair on Thursday made a rallying call against Brexit with a speech in which he highlighted the importance of regional alliances to face rising power of large population countries like India and China.

The former Labour prime minister, who had campaigned for Britain to remain in the European Union (EU) in last June's referendum, was equally critical of his own party as of the ruling Conservative government in a speech in here to the pro- European campaign group Open Britain.

He said: "The case for Europe remains rooted not in understanding the past but the future. All over the globe, countries are coming together in regional alliances for a very simple reason.

"As China rises, as India and other large population countries follow and with the USA already so powerful to maintain strength and influence, to defend our interests adequately, nations of our size will cooperate based on proximity," Blair said.

The 63-year-old politician was seen as making a comeback to frontline politics of sorts with plans for a cross-party "movement" to change the UK's mind on Brexit.

"The debilitation of the Labour Party is the facilitator of Brexit. I hate to say that, but it is true. What this means is that we have to build a movement which stretches across party lines," he said.

Blair, who was Britain's prime minister between 1997 and 2007, used the speech to confirm that he will be setting up an institute that works towards countering the pro-Brexit tide.

"Indeed even the term 'Hard Brexit' requires amendment.

The policy is now 'Brexit at any cost'. Our challenge is to expose, relentlessly, what that cost is," he said.

"To show how this decision was based on imperfect knowledge, which will now become informed knowledge. To calculate in 'easy to understand' ways how proceeding will cause real damage to the country and its citizens and to build support for finding a way out from the present rush over the cliff's edge," he noted.

British Prime Minister Theresa May wants to trigger formal Brexit talks by the end of March by invoking Article 50 of the Lisbon Treaty, a move which was backed by House of Commons MPs last week.

Downing Street has stressed that it is "absolutely committed" to delivering Brexit.