Consultants and MPs opposed to plans to close Lewisham's Accident and Emergency department have handed letters and a 20,000-signature petition to Downing Street.
Protesters, including Lewisham East MP Heidi Alexander, say the closure would leave them with one accident department for 750,000 residents.
The planned closure is part of a reorganisation aimed at saving the South London Healthcare Trust after it went into administration.
More top news
Hundreds of people do no know when they will be allowed back home after a 'serious incident' was declared in east London.
A Tube and rail strike planned for Wednesday evening could bring the capital to a standstill causing travel chaos for millions of commuters
The only Muslim survivor of the 7/7 terror attack in London has urged the country to stand together against Islamophobia.