ipr

The warnings about ownership of the IPR came true more than a decade later when Post Office decided to invite other companies to take over the Horizon contract.

He said that if IBM had tried to build new software without any of the IPR from Horizon, it would have needed to "start from scratch, which would have cost the Post Office hundreds of millions of pounds".

"IPR is the reason why the Post Office hasn't been able to move away from Fujitsu and the Horizon software," he said.

The Post Office did not respond to the BBC's specific questions about IPR being the reason why the company was unable to ditch Fujitsu, and said it would not be appropriate to comment ahead of the Post Office Inquiry's final report.

The document says that ICL was "not prepared to... give perpetual licences for all the IPR".