A pilot of the new Horizon Online system at Royal Mail has been scaled back after connectivity problems and outages.
A memo and an e-mail from the company to sub-postmasters said the roll-out of the new system has encountered "technical issues" that mean branches lose connectivity with the company's datacentre, preventing them from being able to carry out customer transactions.
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The e-mail to an unnamed sub-postmaster says, "To ensure that we minimise any further disruption to the network, we have postponed the migration of further branches to Horizon Online until we have addressed the root causes of the problems."
The system is being piloted in a small number of Crown post offices, which are the branches owned by Royal Mail. The post office branches owned under franchise agreements were due to get the system on 6 May, but the e-mail says, "The Crown Office migrations due to take place on 6 May were postponed because of the system outages you outlined in your e-mail."
It adds that a number of changes and software upgrades have been made that "have had a positive effect on many of the problems experienced".
A memo that appears to have been sent to another branch says, "Due to connectivity problems experienced in existing Horizon Online branches we have taken the decision to postpone your move to the new system while we continue to investigate the root cause of this.
"Whilst disappointing, this is not unusual for a major IT project as it enables us to ensure that these issues are ironed out before we proceed with further branches."
The unnamed sub-postmaster had expressed concerns about possible losses in the accounts that might occur as a result of the Horizon problems, and being held responsible for the discrepancies.
It is not the first time sub-postmasters have raised concerns about the integrity of the system and deficits which they say are unaccounted for, but the Post Office has always insisted the core technology is sound.
The Post Office said, "We are piloting our new retail system, called Horizon Online in a small percentage of the branches that make up our network and these pilots have yielded useful information which we are using to streamline further the planned national roll-out of the system. However, the accuracy and integrity of the Horizon system remains intact and the upgraded system continues to be extremely robust and successfully records millions of transactions each day and there is no evidence pointing to any fault with the accuracy of the technology."