Sterling slid to its lowest level in more than three decades against the US dollar today, as investors sold the currency on worries over the impact of Britain's looming departure from the European Union.

Sterling skidded more than 1% yesterday on the back of Prime Minister Theresa May's announcement on Sunday that the formal process that will take the UK out of the EU will start by the end of March.

It has now extended those falls, slipping more than half a percent to $1.2764, its weakest since June 1985.

It also hit a three-year low of 87.51 pence against the euro – down 0.2% on the day.

After the formal 'Article 50' legal exit process is triggered, Britain and the EU will enter an initial two-year negotiating period.

Meanwhile, Prime Minister Theresa May said today it was important to set out the timing of Britain's exit from the European Union to reassure businesses after sterling plunged in the wake of her announcement of the deadline.

"Businesses and people here in the UK want some degree of clarity as to when that timing is going to be," she told ITV's Good Morning Britain show.

"I want to give people more certainty so we will see a much smoother process as we enter those negotiations."