The information watchdog is to grill the Ministry of Defence over its data protection policies after it lost the personal details of 600,000 people.
The laptop, similar to the one in this picture, was stolen on 9 January
Defence Secretary Des Brown will also speak in the Commons next week about the latest loss of personal data, which went missing when a laptop was stolen.
The data includes passport and National Insurance numbers and bank details.
They relate to people who had expressed an interest in, or joined, the Royal Navy, Royal Marines and the RAF.
Information Commissioner Richard Thomas said the MoD laptop incident was "a stark illustration of the potency of personal information in a database world".
"We will require satisfactory answers from the MoD about their data protection practices and a firm assurance that steps have been taken to improve these practices before deciding on the appropriate action to take," he said.
Separately, hundreds of documents containing sensitive personal data have been found dumped on a roundabout in Devon.
Details of benefit claims, passport photocopies and mortgage payments were included in the confidential data found near Exeter Airport.
Last November, it emerged that 25m child benefit records had been lost after HM Revenue and Customs (HMRC) sent two unregistered and unencrypted discs to the National Audit Office.
The MoD said it was treating this latest theft with the "utmost seriousness".
The police said they received a report that the laptop had been stolen from a car parked in Edgbaston, Birmingham, on 9 January.
"The information held is not the same for every individual," the MoD said.
"In some cases, for casual enquiries, the record is no more than a name.
"But for those who progressed as far as submitting an application to join the Forces, extensive personal data may be held, including passport details, National Insurance numbers, drivers' licence details, family details, doctors' addresses and National Health Service numbers."
Foreign Secretary David Miliband said: "I wish we could all find it easy to legislate against people leaving their laptops in cars at night, but of course that isn't the way one can do things.
"Obviously there will be a proper Ministry of Defence investigation into this and I think that we should wait for the defence secretary to make a statement in Parliament, which I know that he is determined to do."
The missing laptop is a black COMPAQ Evo N600c with a 1.5in silver line running top to bottom, right of centre, and with the words COMPAQ in red ink.
It also has a fixed mouse area with a blue rubber cursor button between keys.
The black left rubber foot on the underside of the laptop is possibly missing and one of the catches on the lid is possibly broken.
According to police, the laptop was stored in a black fabric case when it was taken, and it went missing along with a silver Nokia 6030 mobile phone.
HAVE YOUR SAY
The first thing they should do is stop putting the data onto laptops
Llew G, Newbury
West Midlands Police and the MoD refused to comment on from where in Edgbaston the computer was stolen.
An MoD spokesman said: "We are just not able to say where the car was. The details of the location are something for police.
"We are concentrating on looking after the people (whose details were on the stolen laptop) who need reassurance."
The MoD has also said it was writing to 3,500 people whose bank details were on the laptop's database.
It said it was working with the Association for Payment Clearing Services to inform the relevant banks and ensure that accounts affected are "flagged for scrutiny against unauthorised access".
Simon Davies, from pressure group Privacy International, told BBC News 24 he was "flabbergasted".
"I cannot believe that our flagship security agency cannot get this right," Mr Davies said.
"The idea that someone could have the computer with the information unencrypted - it is on a par with the HMRC loss."
Shadow defence secretary Liam Fox told BBC News 24: "It's just been too easy for data to go missing recently and we need to look at how to protect the details of the public."
He said he had spoken to Defence Secretary Des Browne and agreed that the matter would be discussed in the House of Commons next week.
Nick Harvey, Lib Dem defence spokesman, said the incident was further proof of the dangers of a national ID card system.
"If anybody is entertaining lingering support for the idea... surely this would worry anybody into realising that you cannot trust any system you invent to store this much data in one place," Mr Harvey said.
Douglas Young, of the British Armed Forces Federation, said: "It really is very, very worrying and I'm deeply concerned to hear this.
"There must be a top level investigation."
Advice for people who think they may have been affected can be obtained by calling a free MoD helpline number on 0800 085 3600.
Anyone with information should contact West Midlands Police on 0845 113 5000.