Around three quarters of staff at the London Ambulance Service are expected to go on strike today between 7am and 11am.
The action is part of an an ongoing row over pay. Four weeks ago 77% of staff joined the picket line in protest at not receiving a recommended 1% pay rise.
LAS says contingency plans are in place to provide a service for London during strike action. The plans include support from the police and military personnel. Ambulances will only be sent to cases that most seriously need paramedic assistance.
If a major incident in London happens during strike action, staff have agreed to return to work.