A "serious gap" in a fire service's terror response due to an industrial dispute could put lives at risk, according to independent inspectors.
Her Majesty's Inspectorate of Constabulary and Fire and Rescue Services (HMICFRS) said it has "particular concerns" about the Greater Manchester service's ability to respond to terrorist attacks.
Inspector of fire and rescue Zoe Billingham said the service has not had the capability to respond to some terror-related incidents since before Christmas because of an industrial dispute.
She said this means Greater Manchester is reliant on Merseyside to provide specialist firefighters if there is a terrorist incident in its region.
She told reporters these specially-trained and equipped firefighters are expected to go into "warm zones" during terror attacks to put out fires and extract casualties
Ms Billingham added: "We are really concerned about Greater Manchester's arrangements.
"Greater Manchester does not itself have the capability to respond to terror-related incidents in that way.
"It says this is because of an industrial relations dispute.
"Manchester is reliant on firefighters coming from Merseyside to provide this specialist support.
"The delay in any emergency service responding to a terror attack could very well cost lives."
She said it is estimated the crews from Merseyside could be mobilised within an hour.
But Greater Manchester's chief fire officer Jim Wallace said the lack of capacity only applies when responding to terrorist firearms attacks and he stressed the service can respond to all other incidents.
He added: "This is an ongoing and longstanding national dispute between the Fire Brigades Union (FBU) and Fire and Rescue Service Employers, which is why we were unable to resolve it locally.
"It is important to stress that this applies to a very specific type of terrorist incident which is thankfully extremely rare but, if it happens in Greater Manchester, we have a contingency in place where we can call on the support of colleagues on Merseyside in addition to our usual operational response.
"Should Greater Manchester face a terrorist attack in all other circumstances, our firefighters stand ready to play their full part in the emergency services response."
The concerns were raised in a HMICFRS report, published on Thursday, which also said new national standards are needed for fire services.
It warned there is too much variation in how fire services in England record and report emergency response times and define what buildings are high risk for fire protection work.
It said "more than a decade of localism" has led to "marked" differences between services.
Ms Billingham said: "We are pleased that fire and rescue services show real strengths in training for and responding to emergencies - this work undoubtedly saves many lives.
"However it is concerning that there is too much variation in how fire and rescue services operate, resulting in a postcode lottery in the standards of service the public receives."
The HMICFRS report recommends common definitions, standards and applications are adopted in four priority areas including identifying and measuring emergency response times, defining high-risk premises for fire protection purposes, and setting how frequently those buildings are checked.
It said the Home Office, National Fire Chiefs Council and Local Government Association should establish a programme of work to make these consistent "as soon as practicable".
It added that by December 2020, this work should be completed or "significant progress made" in the four priority areas.
FBU general secretary Matt Wrack said: "From the start we have tried to discuss national proposals to expand firefighters' roles to cover 'marauding terrorist firearms attacks'.
"We have been willing to take the necessary steps to bring firefighters into the aftermath of terrorist incidents, with the essential protections in place.
"Responsibility for the delay in resolving this rests entirely with fire service employers and central Government who have been complacent throughout these discussions.
"In our view there needs to be much wider planning and preparation for such terrorist attacks. Every firefighter in the country needs to be trained and equipped for any incident they might be sent to."
A Home Office spokesman said: "We are aware of the concerns around Greater Manchester FRS and are working with them to reinstate a specialist team that will provide an immediate response to a terror attack with support from neighbouring services.
"Where the inspectorate has identified improvements are required, we will consider these very seriously and expect all services to make the necessary changes."