Boris Johnson breached House of Commons rules by failing to declare a financial interest within the required time limit, the Commons Standards Committee has found.
The committee said the former foreign secretary failed to register a 20% share of the ownership of a property in Somerset within the 28-day timetable of acquiring it.
It said that the breach followed a previous failure to register a financial interest and demonstrated "an over-casual attitude towards obeying the rules of the House".
It instructed Mr Johnson to meet with the Registrar of Members' Financial Interests in person to receive a full briefing from her on his obligations as a MP to register all relevant interests.
The committee added it would consider any further breaches of the rules as a matter which may call for "more serious sanction".