* UK calls in army to help NHS
* PM Johnson warns of curfews
* Britain tells people: heed our health advice
* More high street names close doors (Adds Johnson statement time, recasts)
By Kate Holton and Sarah Young
LONDON, March 23 (Reuters) - Britain was to announce new measures on Monday to halt the spread of coronavirus, potentially adding fresh restrictions to an already unprecedented clampdown on daily life, as the army stepped in to deliver protective equipment to hospitals.
With some doctors saying they felt like "cannon fodder", the government said the military would help ship millions of items of personal protective equipment (PPE) including masks to healthcare workers who have complained of shortages.
Deaths from the virus in Britain jumped to 335 on Monday as Prime Minister Boris Johnson prepared to lay out new measures in an address at 2030 GMT, which replaces his daily news conference.
In a letter pleading with Johnson to increase PPE supplies, more than 6,000 frontline doctors said they were being asked to put their lives at risk with out-of-date masks, and low stocks of equipment.
Health Secretary Matt Hancock admitted there had been issues but promised action was being taken. He said the army would drive trucks throughout the day and night to get supplies to medical staff.
"It's like a war effort - it is a war against this virus and so the army have been incredibly helpful in getting those logistics so we can get the supplies to protect people on the front line," he told the BBC, saying the health service now had 12,000 ventilators, 7,000 more than at the start of the crisis.
Later on Monday, Britain's lower house of parliament is expected to approve emergency legislation giving authorities sweeping powers to tackle the outbreak, including the right to detain people and put them in isolation to protect public health.
Britain has already brought in a raft of measures to try to curb the virus and on Monday the government advised citizens travelling abroad to return home immediately.
A much-reduced rail service was introduced and jury trials were suspended, just days after Johnson advised people to work from home if possible and ordered the closure of pubs, gyms and leisure centres.
Other businesses were shutting voluntarily as demand collapses.
Fashion and homeware retailer Next said it will close its stores as of 1800 GMT on Monday until further notice, and bakery chain Greggs and department store John Lewis said they would follow suit.
Advice to stay at home and avoid social gatherings went unheeded by millions at the weekend who took advantage of sunny weather to flock to parks and beauty spots, ignoring instructions to stay 2 metres (6 feet) apart.
Emyr Williams, chief executive of the Snowdonia National Park Authority in Wales, said the past 24 hours had been unprecedented.
The government has warned that Britain would face a shutdown with curfews and travel restrictions if people continued to flout the advice.
"We're perfectly prepared to do that if we need to because the objective here is really clear, which is to stop the spread of the virus," Hancock told Sky News.
The closure of non-essential shops came as Britain opened the first part of a 330 billion pound ($384 billion) loan guarantee scheme for businesses to help small and medium-sized firms borrow up to 5 million pounds to deal with coronavirus stoppages.
UK banks are in a "strong position" to further support an economy that will rebound from the epidemic, the Bank of England and leading lenders said in a joint statement. (Additional reporting by Costas Pitas and David Milliken; Writing by Michael Holden; Editing by Guy Faulconbridge, Alison Williams and Stephen Addison)