Windsor's fire station was closed for three nights last week because no crew was available to man it.
The station in St Mark's Road remained unmanned overnight after 8pm on Saturday, Sunday and Tuesday last week.
A fierce campaign was previously run by residents, organisations and the Royal Borough against plans by Berkshire fire authority to close the fire station in Windsor between 8pm and 8am on a permanent basis.
This led to a compromise solution in September last year - the Windsor fire crew was withdrawn at night but it was agreed other crews would fill the gap, subject to their availability.
This has always meant the odd night being missed. But it is the first time three nights in one week have seen the station empty and unmanned.
Fire Brigade Union representative for Windsor, Michael Rowley, said: "Any deterioration in the level of service is going to cause concern. This seriously undermines the service."
Berkshire's chief fire officer, Iain Cox, said this week that a combination of summer leave and Olympic duty, combined with the current freeze on recruitment, had led to firefighters not being available to keep Windsor open on the three nights.
The fire service across the country faces a £2million cut in government funding over the next two years and Mr Cox said the freeze would apply until the authority knew how it would affect the county.
He said: "It would be cruel to take someone on without knowing whether or not we might have to make them redundant.
"We are running tight at the moment."
He said the fire at Old Windsor was reached in nine-and-a-half minutes from Slough - within the accepted time limit.
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