Post Office technology chief Chris Brocklesby is leaving after a year as the project to replace the troubled Horizon IT system faces long delays and rising costs.
Mr Brocklesby was hired on a one-year contract in August 2023 as “chief transformation officer”.
He leaves on 6 September, according to a message sent to Post Office staff by acting chief executive Owen Woodley.
The Post Office has been struggling to replace the Horizon computer system, which is supplied by Fujitsu.
A plan to build new system running on Amazon’s cloud computing system had to be abandoned in 2022, and the company has spent more than £95m on extending the Horizon contract until next April.
The Post Office said the age and complexity of the Horizon system made switching over too costly and technically challenging.
Reports suggest a replacement system may not fully operational until the end of the decade.
Horizon began operating in 1999, after a troubled development, by the company then known as ICL.
But faulty data produced by the system was used to wrongly convict hundreds of sub-postmasters of theft and false accounting, in what became known as one of the biggest miscarriages of justice in British history.
And inquiry into the scandal is ongoing.
The Post Office asked IBM to build a replacement system to Horizon in 2015, but that project was abandoned.
A spokesperson from the company, which operates as a private business but is wholly owned by the government, said Mr Brocklesby had helped to transform technology in the firm, “providing a strong foundation for the work to replace Horizon and setting up the wider business for long-term success”.
The Post Office said pilots for the new system were currently working in five branches, and it has requested cash from the Department for Business and Trade fund the project to replace it.
“Post Office and the Department for Business and Trade are working on this request and as and when an agreement is reached, we will inform our Postmasters,” the company added.
Mr Brocklesby will be replaced by the former Camelot transformation director Andy Nice.