In 2012 the Daily Mail gave us a breakdown of the bill...
Scotland Yard confirmed it is costing £11,000 every day to ensure the Australian does not flee his bolthole at the Ecuadorean Embassy.
At least four Met officers guard the embassy, on the second floor of a block of flats behind Harrods in Knightsbridge, West London, around the clock
Officers from every London borough, specialist police units and undercover squads have been brought in to join the open-ended stake out.
One colleague said: ‘The officers are being moved around every three or four days to stop the boredom setting in.
‘There are certainly plenty of other things these officers could be doing than standing there around the clock.’
http://www.dailymail.co.uk/news/article-2211530/Police-stakeout-Assange-tops-1m-costs-11-000-DAY-ensure-doesnt-flee-Ecuadorian-Embassy.html#ixzz3AkrOyNy6
£11,000 for 4 officers works out at £2,750 per officer each day. Seems rather a lot when a normal PC gets £70 a day.