Problems with the Bacs clearing system have left up to 400,000 UK workers without their wages, according to PC Advisor's sister title

The database problem was discovered on Wednesday (28 March) when batch-processing which should have been completed failed to clear. Payments due today won't now clear until next week.

Bacs (originally an acronym for Bankers Automated Clearing Services) provides a central clearing house for automated payments. It passes some 30 million payments each day.

It's one of the largest automated payment systems in the world, processing more than 20 million salaries a month, 70 percent of UK household bills and the majority of state benefits and pension payments. In Europe Bacs processes more than 15 percent of all European automated payments.

The Association of Payment Clearing Services, which overseas the Bacs system, said this was the first such problem it had incurred in 10 years.

Voca, which operates the Bacs system, last year completed the transfer of its core systems to an IP-based system Bacstel which, it said brought "improved security, faster payment confirmation, reduced processing costs and the ability to track the status of payments online".

The Bacstel payment engine uses Oracle 10g database and the BEA Weblogic 8.1 application server running on a cluster of clusters of Sun Fire 25000 Ultrasparc servers. The system was built in Java by an in house team supported by software developers from Perot systems.

Earlier this month Voca and Link, the banking network operator, announced plans to merge, creating Europe's largest processor of direct debit and credit transactions.