Emergency planners in Oxfordshire say plans to evacuate London after a terror attack should only be used as a last resort.
A mock terrorist exercise was held in London in September
The county council's emergency planning team has been working on Operation Sassoon, which would see train stations outside the capital receiving Londoners escaping a disaster.
Plans have also been put in place for evacuation by road, with specially designated reception points to deal with travellers.
But councillors fear the local infrastructure may not cope with the volume of people leaving the capital.
John Kelly, the county council's emergency planning officer, said: "We have agreed to provide whatever is available at the time but the expected number of evacuees is far beyond what we have dealt with in past evacuations.
"We have stressed to the London Resilience Team that evacuation should be used as a last resort and only in the most catastrophic of circumstances.
"We advocate a stay-put policy and would not expect this plan to be activated for an event such as the loss of power in the capital."
A mock terrorist attack was staged in London in September to see how emergency services would cope.
The exercise, centred at Bank tube station on the London Underground, involved fire, ambulance, police and medical staff.