STAFF at Brentwood Borough Council spent a total of nearly nine weeks on Facebook last year.
The council's 300+ employees visited the social networking website on 659,762 occasions for a combined 1,486 hours, 53 minutes and 28 seconds between April 2011 and April 2012.
Over the same period, staff spent nearly 19 weeks on the photo-sharing website Flickr, 10 weeks on the BBC website and four weeks on the micro-blogging site Twitter.
Other popular destinations included www.localgov.co.uk, a news website for local government workers (six weeks) and a lettings website called CB Lettings (two and a half weeks).
The websites of Debenhams and River Island were also among the 100 most visited sites, as was property site www.rightmove.co.uk.
Pressure group The TaxPayers' Alliance said: "Council employees are meant to work for taxpayers, not spend their time surfing the web for property.
"Despite the council's guidelines, the sheer amount of time spent by staff on Facebook will leave many with the suspicion that it is not simply being used outside of working hours.
"Only a small number of staff need to use social media as part of their jobs, others should tweet in their own time.
"These are taxpayers' resources and time being used. Local authorities need to tighten up the rules to prevent their misuse."
A council spokesman said: "We have a clear internet usage policy and we monitor it regularly to ensure no breaches.
"We take action if too long a time is spent inappropriately on the internet.
"We have rarely found that we have needed to do this but we have acted firmly on the very few occasions when it has been necessary to resolve a problem.
"Facebook is used an average 1.2 mins per employee each working day and it is used to promote council events and for other business purposes too – that's within our policy."
Council leader Louise McKinlay added: "We need to be adult enough to appreciate that the internet has a part to play in modern-day lives.
"Not only is it used for legitimate council business – and that includes Facebook – but staff may also use it during lunch breaks or after work, which they often do, in between the working day finishing and a council meeting starting in the evening."