The Met released a statement this afternoon confirming they had received a request from the House of Commons «to investigate the alleged unauthorised disclosure of information relating to members» allowances». (politics.co.uk)
However, data breach also covers unauthorised disclosure and unauthorised access to personal data. (educationbusinessuk.net)
Moreover, unauthorised disclosure of commercially sensitive information (eg, trade secrets) may qualify as a criminal offence. (globalinvestigationsreview.com)