London, Oct 3 (IANS): The pound sterling was the worst performer among major currencies on Monday, after British Prime Minister Theresa May said Britain would kick off the process of separating from the European Union (EU) by the end of March 2017.

Speaking at the Tory party's annual conference here, Theresa May ended weeks of speculation and revealed that she will launch formal Brexit talks with EU leaders before the end of first quarter of 2017, meaning Britain is set to leave the EU by summer 2019.

The pound sterling was the worst performer among major currencies, down 0.3 per to $1.2938 as of 6.46 a.m in London. This was the currency's lowest performance since August 16, which has fallen more than 12 per cent against the dollar to levels last seen in 1985 since the British referendum on Brexit in June, the Independent.uk reported.

Kathleen Brooks, Director of research at City Index, said Prime Minister May's speech, which seems to suggest that she is veering towards a 'hard Brexit', is likely to come "at the cost" of a period of economic disruption. 

This is "likely to be negative for the pound," Brooks wrote.

But speaking to delegates on Sunday, Theresa May claimed people who talk about a "trade-off" between controlling immigration and trading with Europe are looking at things the "wrong way". 

"I want it [the deal] to give British companies the maximum freedom to trade with and operate in the Single Market -- and let European businesses do the same here."

"But let me be clear. We are not leaving the European Union only to give up control of immigration again. And we are not leaving only to return to the jurisdiction of the European Court of Justice," she said.

The EU is the UK's biggest trading partner.