The pound fell sharply on Friday (23 September), dipping below the $1.30 threshold, after Boris Johnson suggested Britain will start formal Brexit negotiations early next year.

"By the early part of next year, you will see an Article 50 letter which we will invoke and in that letter I am sure we will be setting out some parameters for how we propose to take this forward," the foreign secretary told Sky News.

Sterling had received a boost on Thursday afternoon after the Bank of England policymaker Kristin Forbes said she saw no need for another interest rate cut following a brighter spell of economic data.

However, the UK currency swiftly relinquished its gains and, by mid-afternoon, was down 0.78% against the dollar at $1.2967 and lost 0.91% against the euro, exchanging hands at €1.1561.

"The present expectations are for the British pound to be maintained at what are historically depressed levels for a prolonged period," said Jameel Ahmad, chief market analyst at FXTM.

"There is still an anxious road ahead once the UK government actually makes the turn towards beginning to exit the European Union,"

Elsewhere, the dollar was unchanged against the yen, fetching ¥100.76, but declined 0.07% against the euro, exchanging hands at 0.8931 euro cents.

"Neither the Bank of Japan, nor the Federal Reserve, sprang any significant surprises this week, but the market reaction was, nevertheless, to halt and for now reverse the rise in bond yields and the dollar's rally," said Kit Juckes, head of forex at Société Générale.

"We're back to yield-hunting and back to that odd world where the strongest currencies are a mix of some of the highest-yielding of the majors – rand, rouble, real – and the lowest-yielding [such as the] yen ."