London's Air Ambulance is to operate 24 hours a day, seven days a week, after the organisation secured new funding.
Until now the service has only operated through the night at weekends using a car. The service has closed between 0100 GMT and 0700 GMT on weekdays.
But London Ambulance's decision to fund the wages of all paramedics means the car service will go full time.
In 2009 the air ambulance attended 1,741 missions, 410 of which were at night.
'Keep Londoners safe'
The registered charity has only been able to fund a 24-hour service at weekends, using specially equipped rapid response cars to cover all after-dark missions, when the helicopter goes off-line.
But now the rapid response car service will also run through the week. The new 24-hour service will start on 1 March.
Consultant Dr Gareth Davies said: "The decision by the London Ambulance Service to fund our paramedics means that we can become the first air ambulance service in the UK to provide medical teams around the clock.
"The extra funding will prove to be invaluable for our service, which is dedicated to helping keep Londoners safe day and night, every single day of the year."
Typically air ambulance crews attend to the most serious cases in London, such as shootings, stabbings and the worst traffic accidents.
The charity is part-funded by the NHS but also relies on public donations.