A number of serving or former military personnel whose personal and financial details were on a laptop stolen in Birmingham last month are considering suing the Ministry of Defence under the Data Protection Act.

More than 600,000 names of those who had either joined the RAF, Royal Navy or Royal Marines or expressed an interest in doing so since 1997 were on the unencrypted hard-drive taken from a parked car on January 9. The information also included thousands of home addresses, individuals' bank details, passport and National Insurance numbers, leading to fears of identity theft or the targeting of armed forces' personnel by terrorists.

The MoD then admitted that two other laptops containing similar recruitment information dating back as far as 1969 had also gone missing in 2005 and 2006. Neither has been recovered.

One, stolen in Edinburgh, contained details of 500 soldiers, while the second, taken in Manchester a year later, held naval and RAF enlistment data. The MoD has now sent warning letters to everyone it believes might be at risk, although, as reported by The Herald this week, many of these letters arrived at out-of-date addresses.

One potential victim who contacted the paper said: "Having had my details confirmed as being on the laptop, including some very personal data, I am now making a formal complaint to the Information Commissioner and wish to seek legal action against either the MOD or the individual responsible for losing the laptop."

A second, who originally enlisted from Eire, added: "My case is already in the hands of my lawyers. The MoD had no right to allow anyone to be so cavalier with personal details."