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Let's get a quick update on Twitter shares now - they ended the day 12% ahead.

They had surged by more than 18% in early trade on the news that the company had reported its first quarterly net profit.

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Explaining the big falls Jonathan Corpina, senior managing partner with Meridian Equity Partners in New York said: "The dust hasn't settled yet, and I think both buyers and sellers are trying to figure out what this market really wants to do.

"I would think that this continues to happen for the next few trading sessions for everything to kind of get flushed out."

To put those fall on Wall Street into context both the benchmark S&P 500 and the Dow have fallen by more than 10% from the record highs they hit on 26 January.

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Female prisoners on a cycle mechanic training scheme launched by Halfords have gone on to work for the retailer after finishing their sentence, it has emerged.

The Halfords Academy was launched a year ago at HMP Drake Hall, Stafford, aimed at women inmates who wanted to train as bike mechanics. It followed a similar facility set up in 2015 at Onley Prison in Rugby, which has also seen offenders offered full-time jobs.

Halfords said two women had joined the company as cycle mechanics following their release, another two are due to start employment soon and others are expected to follow suit. The programme gives offenders the chance to recondition bikes, which are then donated to primary schools.

Jonathan Crookall of Halfords says: "It's about changing people's lives and giving them a second chance. We'd really encourage other businesses to consider supporting offender rehabilitation."

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The falls on Wall Street gathered pace towards the end of trading - with the Dow Jones seeing a big correction after gains earlier this week.

Dow Jones closed down 4.15% or 1,033.23 points to 23,860.12.

The S&P 500 fell 100.58 points or 3.75% to 2,581.

And the tech-heavy Nasdaq was down 3.9% or 274.82 points at 6,777.16.

BBC World

BBC business producer Jonathan Josephs tweets a clip from today's edition of Talking Business with Aaron Heslehurst.

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It certainly has been a rollercoaster ride for sterling today. The pound is back above the $1.39 level to be up 0.3% at $1.3921.

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Nine hundred jobs are at risk at three poultry plants that 2 Sisters Food Group says are "loss-making".

The sites facing closure are Cambuslang in Scotland, with 450 jobs at risk, along with Smethwick and Wolverhampton in England, where 350 and 100 roles are at risk respectively.

Scot Walker, a Unite union representative at the Cambuslang plant, said staff were dismayed at news of the possible closure. "It is far too early to accept that this is the final word," he said.

Last year an investigation by the Guardian and ITV News found that workers at a 2 Sisters factory in West Bromwich had changed slaughter dates to extend the shelf life of meat.

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The Dow Jones has fallen further in afternoon trading in New York to be down 2.3% or about 570 points, but the broader S&P 500 has shed just 1.5%, or 41 points.

Exxon Mobil is the sole riser of the 30 companies on the Dow, with American Express the biggest faller.

"The dust hasn't settled yet, and I think both buyers and sellers are trying to figure out what this market really wants to do," says Jonathan Corpina, senior managing partner at Meridian Equity Partners in New York.

"I would think that this continues to happen for the next few trading sessions for everything to kind of get flushed out."

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Could there be trouble ahead for Tesco? Activist investor Sandell Asset Management plans to oppose its £3.7bn takeover of Booker Group unless the wholesaler secures a better offer from Britain's biggest supermarket.

The New York based hedge fund it has a 1.75% in Booker and that it had conveyed concerns about the Tesco takeover to Booker's board.

Booker shareholders must approve Tesco's offer at a vote for it to proceed.

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Not to be left out, oil prices have also fallen to their lowest in six weeks today after data showed US output had hit record highs, while the North Sea's largest crude pipeline reopened following a lengthy outage.

US crude fell 1.2% to $61.07 a barrel, while Brent also dropped 1.2% to $64.72.

The Bank of England reminds us today that UK productivity levels have been stubbornly flat for the best part of a decade in this handy chart:

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Some of the blame for the slide on Wall Street is being attributed to a fall in returns on Treasuries, or US government bonds, if you prefer.

Bond prices have weakened in recent days as investors prepared for the likelihood of a stronger US economy and higher inflation, which could lead the US Federal Reserve to raise interest rates more times than previously anticipated this year.

That has all kept equity investors nervous about higher rates and inflation. "Now we are having acute attention on what happens in the bond markets, so when yields move up there is an unsettling feeling in the equity market. Things haven't quietened down," said Jason Ware, chief investment officer and chief economist at Albion Financial Group.

"As rates rise, things, as far as equity investors are concerned, are getting worse," he added.

Oops: sterling has now erased almost all of its earlier gains against the dollar to be just 0.1% higher on the day at $1.3893 even.

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While the London market had a reasonably bad day, and Wall Street looking set to close lower as well, it was worse on the continent: the Cac 40 in Paris and the Dax in Frankfurt tumbled about 2% and 2.6% respectively.

David Madden, a market analyst at CMC Markets UK, said: "Stocks are offside today as traders undo the positive move from yesterday. Investors remain unconvinced that panic has disappeared from the markets.

"The aftermath of a major decline usually leaves traders in limbo as they fear another leg lower is around the corner, and stocks are selling off."

Nobel prize-winning economist Paul Krugman comments on today's stock market falls:

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Wall Street is heading south again amid concerns that the US Federal Reserve could soon raise interest rates.

At lunchtime in New York the Dow Jones Industrial Average is down 460 points, or 1.8%, while the S&P 500 fell 1.6% and the Nasdaq Composite shed 1.8% as well.

Analysts said higher returns for US government bonds was the reason for Thursday's drop.

US markets have been under pressure all week due to worries the Fed may accelerate hike rates if inflation rises suddenly.

Samuel Tombs, chief UK economist at Pantheon Macroeconomics, has been taking a close look at what the Bank of England's Monetary Policy Committee said today.