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Robot trading has accelerated this week's market dive and may have sparked the sell-off, experts say.

Financial firms use computers programmed with complex sets of instructions known as algorithms.

They identify trading opportunities and then strike faster than any human could.

Algorithmic trading has become so ubiquitous that some estimate well over half of all trading of the S&P 500 Index is done this way.

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US Treasury Secretary Steve Mnuchin has said he is not overly concerned by the falls on US stock markets.

Answering questions in Congress, he said: "I'm not overly concerned about the market volatility. I think that the fundamentals are strong. There are no systemic issues."

He added that US markets were still up more than 30% since last year's presidential election and called recent fluctuations a "normal market correction".

"Although large, it's just a disconnect," he said, adding there was nothing he would recommend doing about the markets "at this time".

The London market has ended 2.6% lower amid continued volatility on US share markets.

The FTSE 100 index ended Tuesday 193.58 points lower at 7,141.40 points. The worst performers were investment firms Scottish Mortgage Investment Trust, which lost 4%, and Standard Life Aberdeen, down 3.7%.

France's Cac 40 and Germany's Dax indexes both shed around 2.4%, reflecting the sharp falls on US and Asian markets on Monday.

The Eurostoxx 50, which comprises the biggest eurozone companies, lost 2.5%.

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A spokesman for the GRG Business Action Group - which represents more than 500 businesses "put into financial distress" under the bank’s GRG restructuring division - said Clive Lewis's claims were "extremely worrying".

It said the FCA needs to publish in full a report on the matter that has been leaked to several parties, including Mr Lewis and the BBC.

So far the FCA has only published a summary, but has agreed to a Treasury Committee proposal for a legal adviser to study its report in full.

The GRG Business Action Group spokesman said:

"[Mr Lewis ] described the FCA’s published summary as a ‘sanitised version’ of the actual report. In view of the FCA’s repeated assurances that it is not favouring RBS, this is a shocking allegation. [FCA boss] Andrew Bailey will have to explain himself before the Treasury Select Committee tomorrow.

"According to Mr Lewis, the report concludes that RBS’s mistreatment of its business customers was 'systemic and widespread'. Thousands of people whose jobs, livelihoods and businesses were destroyed by RBS’s rogue bankers already knew this. Parliamentarians and the general public deserve to know it too."

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RBS executives "misled" a parliamentary committee over the extent to which the bank mistreated small businesses during and after the financial crisis, an MP has claimed.

Labour's Clive Lewis made the comments after claiming to have read the full version of a leaked report on the matter by the Financial Conduct Authority. So far the FCA has only made public a summary of the report.

"Having read the document I believe it shows that RBS executives misled the Treasury Select Committee in their evidence and had a stated policy of misleading members of this house," Mr Lewis said.

"Far from being isolated incidents of poor governance as they claimed to the committee, this report explicitly states their behaviour was, quote, 'systemic and widespread'."

RBS said: “The evidence we provided to the Treasury Committee accurately reflected the bank’s position. We are not clear on what basis the allegations are being made, but we would strongly deny the suggestion that we misled the Committee.”

The FCA report looked into the conduct of the bank's Global Restructuring Group, which handled over 12,000 struggling firms between 2007 and 2012 and is accused by some of purposely pushing them into bankruptcy to pick up their assets on the cheap.

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As European stock markets follow the turbulence in Asia and US trading, the BBC has asked for your questions about what is happening.

Many of the questions the BBC received focused on the possible ramifications for ordinary people. Others wanted to know if it was likely the instability could bring about a crash.

BBC Business journalist Brian Milligan answers a selection of your questions here.

Anthony Reuben
BBC News

A heads-up from Robert Chote, chairman of the Office for Budget Responsibility (OBR).

Speaking at the Institute for Government, he said he would be able to make more precise forecasts of the financial settlement for when the UK leaves the EU, in time for the Spring Statement on 13 March.

He said there was enough detail in December’s draft agreement between the UK and the EU to be able to come up with some predictions.

While there are areas in which the government might choose to make contributions, which we do not yet know about, he expected to be able to predict things like the levels of contributions to EU civil service pension schemes.

Anthony Reuben
BBC News

Robert Chote, chairman of the Office for Budget Responsibility says the government shouldn't have been surprised that the Treasury's economic forecasts on the effect of Brexit were leaked.

Speaking at the Institute for Government he said that in an ideal world the government would have commissioned the research with the intention of publishing it.

He added that the process could then have been scrutinised by a panel of economists, including at least one person who thinks Brexit is an economic positive.

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The US trade deficit reached its highest level in nine years in 2017, official figures show.

It comes amid efforts by President Donald Trump to re-balance to America's trading relationships.

According to the Commerce Department, the trade gap in goods and services rose to $566bn last year, the highest since $708.7bn in 2008. Imports hit a record $2.9tn, outstripping exports of $2.3tn.

Experts said the import surge reflected America's buoyant economy, with confident consumers buying more foreign products.

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General Motors says its underlying earnings in the fourth quarter were better than expected - although a one-off tax charge drove it into the red.

The car maker reported a net loss of $5.2bn in the period due to a $7.3bn charge linked to recent US tax reforms. Total sales fell by 5.5% to $37.7bn.

But the car maker said strong demand in the US, China and South America helped it achieve higher operating earnings compared with the previous year.

Shares in the firm were up 3.5% in morning trade in New York.

US tax reform has led to a number of losses among US corporations, but there is broad consensus that tax cuts will boost earnings in the long term.

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The FTSE 100 has perked up a bit after US shares rebounded in early trade in New York.

The London market is now about 1% lower at 7,253.72, having fallen more than 2% earlier.

Germany's Dax and France's Cac 40 are on similar trajectories, having recuperated to trade 1.6% lower.

Emma Simpson
Business correspondent, BBC News

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It's an outcome no one could've predicted or either side wanted. It had already taken up more than a quarter of a year and had been beset by delays.

It had been hoped that it would end before Christmas. The judge, Deborah Taylor, became ill during her summing up in January. It's been stop, start, stop ever since.

There was a pause of two weeks to allow a juror to go on holiday. Having already discharged one juror, losing another one would've meant the jury going down to just ten men and women.

And then there's the cost. This has been a complex, multi million pound, trial.

The Serious Fraud Office, which brought the case, will now decide whether or not a retrial is appropriate. Meanwhile the defendants, who denied the charges, have almost another month to wait before they find out what happens next.

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After slumping yesterday, the Dow Jones share index has fallen further at the start of trade on Tuesday.

It opened 2.2% lower but quickly pared those losses to trade down 0.5% at 24,224.5.

The Nasdaq has also pared its losses and is trading 0.1% lower at 6,958.17 points.

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Guy Foster of wealth managers Brewin Dolphin is not wholly surprised by the fall in global stock markets.

“We expected volatility to pick up, as central bankers, who had hitherto been smoothing the path for investors with unnatural amounts of liquidity, have been trying to quietly withdraw their support.

"Interest rates are rising at a time when the economy needs money for the increased corporate investment activity which is taking place. That means there won’t be the constant flow of money into the equity market which has been supporting prices over the last couple of years."

BBC Breakfast

It's 100 years today since some women got the right to vote. But equality isn't just about voting, it's an important value to have in the workplace too. BBC Breakfast's Steph McGovern met women who've reached the top of their fields - Inga Beale, chief executive of Lloyd's of London and retail guru Mary Portas - to get their advice for women just starting out in their careers today.

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The pound is down again today. It's 0.7% lower against the dollar at $1.3859 and 0.5% lower against the euro at 1.1228 euros.

Alex Scott, chief strategist, Seven Investment Management, has commented on the current market volatility.