The Passport Office chief executive Paul Pugh said the agency was facing a challenging situation the like of which has not been seen in recent years, after apologising for the delays.
He said the Passport Office is dealing with 480,000 applications. Around 90% are being processed within targeted time.
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The Ukip leader confirmed he had "no prior warning" of Douglas Carswell's resignation from the party as he hit out at the "staunch Tory".
Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.
The violence began after a counter-protester allegedly doused a female rally organiser with pepper spray.