Mitchell, of Ramsgate, Kent, and Wayne Morris of Margate, Kent, were jailed for three years after pleading guilty on 19 January at Canterbury crown court to conspiring to defraud.
Because the men were not present in court, they still have the right to apply to the appeal court for a greater reduction if they think a 12-month cut is not enough.
Judge James Rant, sitting with lord justice Potter and Sir Brian Smedley, said the victim of the fraud involving claims for council tax refunds was Thanet DC.
Refunds would apply in cases such as a house being left empty because someone had died, he told the court.
Mitchell, who had worked for the council since 1982, was an officer involved in verifying applications for refunds.
'He was not responsible for the final authorisation but he prepared all the documents, signed them and passed them on. His claims generally were taken at face value,' said the judge.
'He was the insider without whom this fraud could not have taken place.'
Morris had known Mitchell for 25 years. The fraud involved locating a member of the public who had a bank account and who would be prepared to accept a cheque into it.
In some cases Morris turned to family members, other times he went further afield.
Sometimes he pretended his own account was frozen and got a person to agree to putting a cheque through their account, 'keeping a certain amount for their trouble.'
Judge Rant said a number of these people later were asked by the council to repay the money while others were cautioned.
One case involved Morris meeting a woman at a Ramsgate casino. He told her his bank account was frozen and offered her£50 if she passed a cheque through her account. She agreed and provided the necessary details.
Mitchell completed the council forms, verifying the council tax rebate of£662.30, claiming the woman had been living somewhere else looking after a sick relative.
The fraud took place between August 1998 and June 2000, and involved 47 cheques totalling£35,928.58.
The matters came to light when one cheque recipient expressed her concern to someone at the council and the matter was investigated.
Judge Rant rejected claims that Morris's sentence should be cut by more than Mitchell's, saying he had 'taken full advantage' of Mitchell's gross betrayal of his employer's trust.
'He persuaded members of the public to become involved,' he said.
'The part played by each was necessary and mutually supportive to the other for this scheme to succeed.'
Describing the fraud as 'sophisticated, persistent and carefully planned,' the judge said it involved public funds.
STRAND NEWS SERVICE