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"Following a request from the first minister, I consider the current situation facing the Welsh steel industry to be of urgent public importance, and have therefore decided to recall the assembly on Monday 4 April.
"It is now important that Tata act as a responsible seller and provides the workers and both governments sufficient time to demonstrate the viability of steel making at Port Talbot.
"I urge Tata not to abandon steel making at this early point but to support the efforts of the workforce and governments to establish an attractive business for future investors."
MEP Mr Gill has criticised the UK government which he claims has "gold-plated EU legislation all along making it harder and harder for these kinds of industries to survive".
Labour leader Jeremy Corbyn will visit Port Talbot this afternoon, union representatives say.
"The EU is our most important market for steel," says the Britain Stronger In campaign ahead of the UK's EU referendum in June.
Overall, our steel industry is better off as part of the EU - as a bloc we can act against steel dumping far better than we could on our own and get the best deal for our steel industry in their biggest market.
The town of Port Talbot has for more than 60 years been synonymous with steel.
In its heyday in the 1960s, nearly 20,000 people worked there and the town grew up around it.
Numbers may have dwindled, but it still has an imposing presence in the Welsh economy.
Tata Steel employs more than 80,000 people worldwide and is part of the wider Tata Group, an Indian conglomerate.
Founded more than 100 years ago, it has grown into a global producer with operations in 26 countries and revenue of around £15bn last year.
It became Europe's second largest steel producer, and the biggest in the UK, after it bought Corus, formerly British Steel, for £8bn in 2007.
Tata also has plants in the Netherlands, Germany, France, Belgium and south east Asia.
The steel it produces is used to make a huge range of products, from cars to office furniture and battery cases.
Almost 20,000 people are employed in the steel sector, and more than one in six are now either losing their jobs or at risk of losing them. Business reporter Tim Bowler looks at the issues facing the industry.
Political editor, Wales
The key question is whether the Welsh Government can do something other than providing the usual level of support for regeneration and training for workers who have lost their jobs.
The Scottish government recently bought two mothballed steel plants in Lanarkshire from Tata before selling them to a private company on the same day.
First Minister Carwyn Jones has said he'd consider something like that but admits there are major differences in the scale.
The buy-out in Scotland will secure around 200 jobs. In Port Talbot we are talking about thousands, and the future of the biggest steel plant in Britain.
Leader of the Welsh Liberal Democrats, Kirsty Williams, said: "Many of our communities strongly rely on this industry. We must stand up for them, learn lessons from the past, and take strong action now.
"The Liberal Democrats believe the UK Government must be prepared to temporarily re-nationalise at least part of the plant in order to make sure that it can be passed as a going concern to a new investor and prevent a gap in operation," she added.
UKIP's leader in Wales, Nathan Gill, described the news as "heartbreaking".
"It is a tragedy though that those in a position to change policy to help this industry do not recognise the magnitude of this decision by the company.
"Port Talbot and its people stand to be massively hurt by this decision unless it is reversed whilst there is still time. Generations will find it more difficult to find work, buy homes and build careers."
BBC Business Editor
Tata says it wants to sell up “in a time bounded way” - in other words pretty damn quick - understandable if you are losing a million pounds a day.
It insists it’s not leaving the business in the lurch and points to the Liberty and Greybull transactions as evidence.
They may buy additional bits and pieces but there is deep scepticism that either of them have the firepower or appetite to take on something as big as Port Talbot and its 4000 workers.
1902: The first steelworks at Port Talbot is founded
1923: A second Margam works is finished
1947-1953: The third Port Talbot plant is built and becomes part of Steel Company of Wales. The works employ around 18,000. By this period, the rolling mill at Ebbw Vale has become the biggest of its kind in Europe.
1962: The Queen opens the £150m Spencer works in Newport, later known as Llanwern.
1967: British Steel is formed from 14 different firms as the industry is nationalised
1980: 6,500 people lost their jobs at Shotton Steelworks, Deeside
1988: British Steel is privatised and becomes part of Dutch-owned Corus in 1999.
1990: More than 1,100 jobs are lost at Brymbo steelworks in Wrexham.
2001: Corus announces 6,000 UK job losses - a fifth of its workforce. They include 1,340 at Llanwern in Newport, and 90 at Bryngwyn in Swansea. The Shotton cold strip mill closes with 400 redundancies.
2002: The Ebbw Vale steelworks shuts with 850 job losses, although 300 workers move to other plants.
2007: Corus bought by Tata Steel of India
2014: Tata blames high business rates and "uncompetitive" energy costs for 400 job losses at Port Talbot.
2015: Tata Steel reported a "turbulent year" due to Chinese exports and high energy costs but Port Talbot produced an all time record of 4.19m tonnes of hot metal while the hot strip mill hit speed-of-work records. In August, it mothballs part of its Llanwern plant for the third time in six years, with 250 job losses.
The man in charge of Tata's European operations said the firm wants a buyer to continue steelmaking at Port Talbot.
Koushik Chatterjee said: "We have been in discussion with government in terms of finding out a desirable outcome and we will continue that engagement and we will see where that goes.
"We would like a buyer to come in and continue the business and maybe have a different risk profile than what we have gone through and perhaps continue to sustain the business, and that would be a happy moment for us.
"We have over-capacity in the steel world, we have a market situation which remains challenging and the currency has not helped.
"Hopefully we will find a buyer who sees value in this business and continues."
Assistant political editor
Tata Steel says it cannot give an "open ended" commitment to keep steel plants in the UK open while a buyer is sought.
The company says it wants to "move quickly" to secure a sale but ministers have warned they need months - not weeks - to search for a buyer.
They point to the example of the Scunthorpe steel plant where it took more than a year to find a potential buyer.
The company's executive director Koushik Chatterjee declined to say how long he would give the UK Government to secure a buyer.
Mr Chatterjee also defended Tata's running of the UK steel plants. He said the firm had supported them for nine years and lost more than £2bn.
He said so far they had not spoken to any potential buyers. He said the steel industry was facing "unprecedented challenges" because of over-capacity.
The letter from First Minister Carwyn Jones to Presiding Officer Rosemary Butler requesting the recall of the assembly reads:
In accordance with Standing Order 12.3, I formally request a recall of the National Assembly so that members are able to consider the implications of Tata Steel's decision in a full plenary session. I intend to make an oral statement and my preference is that the Assembly should meet on Monday 4th April.
This is the scene outside the plant in Port Talbot this morning
Unite Wales has issued a statement:
Steelworkers cannot afford the government to keep dithering over intervention in this vital UK industry. Ministers must honour their promises to keep the lights over the UK's steel communities burning. Tata, as well as the UK and Welsh Government, must also do all in their power to have these vital assets handed back to this country in a shape that allows a serious buyer and a future to emerge.
The UK Government is looking at all "viable options" to protect the future of Port Talbot steelworks and Tata's other UK sites, said Welsh Secretary Alun Cairns.
"The government is committed to all it can to explore all viable options to try to save as many jobs as possible and to preserve the local strategic interests in areas such as Port Talbot but also the national strategic interest," he told BBC Radio Wales.
First Minister Carwyn Jones told BBC Wales: "We must remember that vast amounts of money is needed to secure the steel industry's future - but we are ready to support any initiative in order to save jobs.
"I call upon Tata to act responsibly in terms of finding a new buyer - they must ensure that the site stays open for an adequate period that would enable a potential buyer to come forward."
He also discussed the possibility of business rate support from the Welsh Government.
"This on its own would not be enough - we also need support of UK Government and investment from outside. But we now know what we are facing - before Christmas we thought that the site would close - so things have changed - at least now we have more options."
Tata employs over 6,000 workers in Wales, according to the Community Union.
In the UK, the figure is just over 15,000.