Organised crime gangs are stealing hundreds of millions of pounds a year from firms by making false changes to records at Companies House, police revealed yesterday.

The networks, many with international connections, submit letters to the business register in Cardiff, requesting bogus changes to legitimate company addresses.

They then redirect a firm's deliveries to the fake address, or order easily disposable consumer goods such as mobile phones or computers for delivery to the fake address.

The criminals collect the goods and sell them on (often to legitimate companies) before vacating the premises - in many cases before the firm has even realised what has happened.

Officially, this type of fraud is estimated to cost British industry more than £50m a year. But business organisations and police acknowledge the true cost is much higher.

Many firms are reluctant to own up to being a con victim, for fear of harming their reputations and shareholder confidence. Firms supplying goods do not get paid, and there is a knock-on effect in terms of higher costs, job losses, and, in some cases, bankruptcies.

Now Scotland Yard has joined forces with Companies House in Operation Sterling, an initiative to raise awareness about business identity fraud and encourage firms to use a new, secure online register to change company records.

Tim Moss, director of strategy at Companies House, explained that its staff received more than 25,000 documents in the post every day, requesting changes to details of some of the the 2m UK-registered firms.

"The imperative is to process these changes so business efficiency is not impeded," he said. "But we cannot possibly investigate the validity of all these documents, so the companies need to help themselves.

"We are asking that they sign up to our protected online filing system, Proof, and a monitoring service, which will send firms an email alert letting them know when changes to their details have been requested."

Police and Companies House are also advising suppliers to check potential customers more thoroughly, and be wary of large, unexpected orders.