The Information Commissioner's Office (ICO) has fined the London Borough of Barnet £70,000 for losing records containing confidential information on a number of vulnerable children.
The ICO said the council had failed to comply with an agreement it signed earlier in June 2010 following a similar data loss.
"We issued the fine because the council has not complied with its previous agreement, placing confidential information on a number of individuals, including children, in jeopardy," an ICO spokesman told V3.
"The fine is at the lower end of the spectrum, with the ICO being able to issue fines up to £500,000, but it is still serious."
The ICO said the data lost included the names, addresses, dates of birth and details of the sexual activities of 15 vulnerable children and young people.
The data was reportedly lost in April last year, after a social worker who took a number of paper documents home was burgled. The previous 2010 data loss occurred after a laptop containing unencrypted data was stolen during a similar burglary.
At the time of publishing, Barnet Council had not responded to V3's request for comment on the fine.
The ICO spokesman told V3 that there are more fines "in the pipeline", though he refused to offer further details.
The fine follows on from information commissioner Christopher Graham's InfoSec warning that people will no longer tolerate companies and government bodies playing "fast and loose" with their personal data.