The Information Commissioner's Office (ICO) has carried out its second raid in three months on SMS spammers, confiscating 20,000 SIMs allegedly used by a Manchester firm to bombard mobile users with ambulance-chasing claims messages.

The raid comes after the ICO conducted a similar swoop on in December which led to the same number of SIMs being taken out of service.

The unnamed business is accused of operating 'SIM banks', hardware systems devices that automatically send large numbers of messages from unregistered pay-as-you-go SIM cards.

It is believed that millions of these messages are now sent each day to UK mobile users from as part of campaigns to harvest the mobile numbers of users unwise enough to reply, selling them on to claims marketing companies.

Familiar messages include the infamous "Our records indicate that you may be entitled to compensation of £3750 for the accident you had," which many mobile subscribers have received at some point in the last three years.

The hook is the offer to desist if users text 'stop' to a four-digit number but that is merely a ruse to get a response from the unwary. Anyone replying will be verifying their number, after which spammers resell them in bulk to claims marketing companies.

The unfortunate users will then likely be deluged with repeat messages regardless of whether they send 'stop' messages' or not.

"Once they [spammers] have trapped your number they will then sell it into the [claims] industry," ICO investigation's manager David Clancy told the BBC after the latest raid.

"First users will pay £1, £1.50 for that phone number. A month later it will be distributed to lots of organisations for 50p, 20p, 10p a time. It makes a lot of money."

In May 2011, the ICO was given the power to fine companies that break the Privacy and Electronic Communications Regulations 2003, but has clearly decided that fines alone won't have enough effect on a wily industry that can shut down its operations before opening them in another guise using new SIMs.