Hospitals have been told to prepare for a possible Bank Holiday terror attack this weekend.
It comes after security was stepped up around the country following the Manchester Arena atrocity which killed 22 people including an eight-year-old girl.
Staff in 27 cities were urged to be ready to deal with an incident in a letter obtained by the Health Service Journal.
They were also asked to ensure they knew what to do if their hospital went into "lock down".
The letter from national clinical director for trauma Chris Moran read: "You will be aware that we have a bank holiday weekend approaching.
"There are a number of things that all trauma units and major trauma centres can do to prepare for a further incident and I should be grateful if you could disseminate these within your network so that front line clinicians are aware."
The terror threat in the UK remains at critical - the highest level - after Monday's bomb blast at an Ariana Grande concert.
Armed police have begun patrolling trains and transport hubs across the UK for the first time in the wake of the Manchester attack.
Nearly 4,000 soldiers could also be deployed to support police in heir security operations as part of the Government's Operation Temperer.
The plan is designed to bring in members of the army to protect sites at risk of attacks such as transport hubs, stadiums and key landmarks.
Prime Minister Theresa May said they may also be deployed at major sports or entertainments events like the FA Cup final at Wembley on Saturday or the Champions League final in Cardiff on June 3.
All troops on the streets will be working under the command of police officers.
Police have told tens of thousands of people heading to Radio 1's Big Weekend music festival this weekend they have applied for extra armed support for the event.
The two-day music festival - headlined by Katy Perry, Little Mix, Kasabian and Kings Of Leon - will see more than 50,000 people gather at Burton Constable Hall, near Hull, on Saturday and Sunday.