The purchase, storage, maintenance and upgrade work on the cannon cost £322,000, including £20,000 on repainting, £5,000 on bodywork repairs due to corrosion and almost £1,000 on installing radio and CD players for the drivers.

It is understood that the stereos, which included radios and CD players, had been installed to enable police officers operating to listen to the news while operating the vehicles 'in the field'.

Other costs incurred in the modification and maintenance of the machines between April 2014, when they were bought, and April 2016 include:

£30,625.96 for conversion to UK specification and service parts

£19,376.70 for the supply and fit of CCTV

£8,584.50 for the supply and fit of warning equipment

£3,109.20 for the supply and fit of 999 sirens

£1,688.04 on MOT tests

It is thought that the vehicles could fetch as little as £2,000 each when they are sold, despite the Metropolitan Police wanting £43,000 for each of them. The GLA will save almost £175,000 over the next eight years by seeling the vehicles, officials have claimed.