Contractors at Revenue and Customs in Southend are being paid up to £1,000 a day - despite hundreds of civil service jobs being under threat.
Furious union officials say the huge wages for the IT jobs, based at Alexander House and Portcullis House in Victoria Avenue, Southend, are a gross waste of taxpayers' money.
Sources at the Public and Commercial Services union say the wages are an "insult" to the estimated 340 people who face having their jobs cut at the tax office.
An Echo investigation has revealed there are around 200 contractors and consultants working from Southend, earning an average of £650 a day.
Some consultants are being paid a daily rate of more than £1,000.
A union source said: "People are being conned. Personally, as a taxpayer, I am absolutely furious. Not only are the services going down in quality, but we are paying vast amounts for it.
"You can see the difference between the civil servants and the consultants in the car park.
The consultants are all driving BMWs, Mercedes and Porsches.
The civil servants who earn nowhere near the same amount drive Fords."
Union members are currently being balloted on whether they will take industrial action in protest over pay, pensions and the privatisation of the civil service.
The source said: "I am worried about the effect on the Southend economy.
"There will be fewer opportunities for people coming out of university to go into these more skilled jobs because they have been given to outside consultants and private companies.
"That will affect businesses in the town because people are coming in from out of the area and don't spend as much money here."
David Amess, MP for Southend West, was scathing about the employment set-up at Revenue and Customs.
He said: "This is yet another example of Southend being treated unfairly.
"The amount of money being spent on consultants when we are being told that the Treasury is trying to save money is ridiculous.
"I will continue to raise the issue in Parliament."
Maddy Ratnett, spokesman for HM Revenue and Customs, said he was unable to give specific details about wages due to confidentiality.
He said: "HMRC only employ consultants when specific skills are required and we do not have - or cannot quickly develop - the necessary skills in-house.
"Sometimes the range of our projects, some of which can last for many years, and the changing role of the organisation, necessitates both short-term through to long-term specialist support.
"We are working to ensure that in areas where we do use consultants, we transfer the relevant skills to HMRC staff for the future."
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