The pound has dropped to a 31-year low as investors fret over the British government's suggestion it will focus on controlling immigration in its talks to leave the European Union.

Sterling dropped to below 1.28 US dollars on Tuesday, days after British Prime Minister Theresa May clarified the timeframe for Britain's exit from the bloc, saying she will trigger two years of formal exit talks before April.

But members of her governing Conservative Party are wrestling over control of the steering wheel that will take Britain toward either a looser but still intertwined relationship with the bloc, or a dramatic "hard Brexit" with unknown consequences.

Hard-core Brexiteers believe regaining control - over financial rules, business regulations and especially over immigration - is more important than remaining in the EU's single market or customs union.

The EU insists Britain cannot choose to benefit from access to the single market without also keeping open its borders to EU citizens.

Markets analyst Michael Hewson said the tone of May's remarks suggested Britain could be veering towards a "hard Brexit" and markets reacted over the "perception that could cause a significant amount of disruption."

Hewson said there was scope for further Sterling weakness, especially against the US dollar with the potential for the Federal Reserve to raise interest rates by December.

London - 4 October 2016

1. Entrance of CMC Market in the City of London

2. Various of screens showing live currency and stocks exchanges

3. Various of analyst Michael Hewson talking to a colleague then walking by

4. SOUNDBITE (English) Michael Hewson, Chief Market Analyst at CMC Markets:

"Theresa May, UK Prime Minister, basically told the markets that she intended to trigger article 50 of the Lisbon treaty by the end of Q1 2017 and that wasn't really a surprise. I think what was the surprise was the tone of her remarks. The tone of her remarks suggested she really wanted to take control of immigration and that has led markets to join the dots and essentially speculate on the fact that she could be looking for what is termed a hard Brexit, i.e. a pull out from the single market. And I think there's a perception that could cause a significant amount of disruption."

5. Cutaways of Hewson

6. SOUNDBITE (English) Michael Hewson, Chief Market Analyst at CMC Markets:

"I certainly think there's scope for further sterling (pound) weakness particularly against the dollar because there's an awful lot of speculations and the Federal Reserve may well raise interest rate in December so from that point of view the Federal Reserve is potentially on a hiking cycle so that could pressure the pound. Against the euro yes we could see potentially a little bit more weakness but Europe has problems all of its own, particularly in the banking sector. So I think the downside for Sterling against the euro could be far more limited than it is say against the US dollar."

7. Various of people working in the office