* Coronavirus death toll in Britain jumps to 422
* People who flout new restrictions face fines
* Temporary hospital in London to open next week
* Government calls for 250,000 volunteers for health service (Adds police patrol of rail network)
By William James and Andy Bruce
LONDON, March 24 (Reuters) - The number of coronavirus deaths in Britain jumped on Tuesday, the first day of a national lockdown, while the government called for 250,000 volunteers for the health service and announced a temporary hospital would open in London next week.
In a TV message on Monday evening watched by more than 27 million people, Prime Minister Boris Johnson ordered people to stay at home, told nearly all shops to close and banned social gatherings including weddings and baptisms.
However, public transport in London was busy during the morning rush hour and the streets were far from deserted amid confusion over the government's advice to workers.
The death toll from coronavirus in the United Kingdom has jumped by 87 to a total of 422 - the biggest daily increase since the crisis began.
Meanwhile, the economic devastation was underscored by a survey that suggested the economy was shrinking at a record pace, faster than during the 2008-09 financial crisis.
The unprecedented peacetime restrictions announced by Johnson, which will last at least three weeks, are intended to stop the state-run National Health Service (NHS), which suffers from staff shortages at the best of times, being overwhelmed.
"These measures are not advice, they are rules and will be enforced, including by the police," health minister Matt Hancock told parliament.
At a news conference later, Hancock announced plans to open a temporary hospital next week at the Excel Centre, a huge venue in east London normally used for trade fairs and similar events.
"With the help of the military and with NHS clinicians we will make sure that we have the capacity that we need so that everyone can get the support they need," he said.
British Transport Police said 500 officers will be deployed to train stations across the country to remind the public of the government's advice to travel only when essential.
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Hancock called for 250,000 volunteers to help the NHS with tasks such as delivering medicines from pharmacies, driving patients to and from hospital appointments and phoning people isolating at home to check up on them.
"If you are well and able to do so safely, I would urge you to sign up today to help the most vulnerable people in our communities as an NHS Volunteer Responder," Hancock said.
He also said the government had bought 3.5 million coronavirus antibody tests so that people who suspect they have had the virus would be able to find out for sure.
Despite the message for people to stay at home, some roads were still busy and utility workmen and others were still mingling close together.
Social media images showed the capital's underground trains were packed with passengers closer than the 2-metre (6-foot) recommended distance apart and the government said "appropriate" construction work should continue.
"The government needs to urgently provide clearer guidance on who should be working and who shouldn't," said Rebecca Long-Bailey, the opposition Labour Party's business policy chief. "No one should be asked to work if they are not providing an essential function in this crisis."
Under the curbs on movement, people should leave their homes only for very limited reasons such as going to supermarkets for vital supplies or for exercise once a day.
Police, who will be able to issue fines of 30 pounds ($35), will now be able to break up gatherings of more than two people.
A snap YouGov poll found that 93 percent of Britons supported the measures but were split on whether fines would be a sufficient deterrent.
Supermarkets, where shelves have been stripped bare by panic-buying in recent days, said they had begun limiting the number of shoppers in stores at any one time, erecting barriers outside, and installing screens at checkouts to protect staff.
Last week, the government announced billions of pounds of help for businesses and said it would help to pay the wages of employees, giving grants to cover 80% of a worker's salary if they were kept on as staff.
But critics said it did not provide support for the self-employed, who total about 5 million in Britain compared to roughly 28 million employees, meaning they either had to keep working or risk losing all income.
Finance minister Rishi Sunak told parliament the government was working on measures to help self-employed people, but said these had to be practical and fair. (Additional reporting by Alistair Smout, Sarah Young, Paul Sandle, James Davey, David Milliken and William Schomberg; writing by Estelle Shirbon; editing by Stephen Addison)
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