British Bangladeshi MP Tulip Siddiq, Economic Secretary to the Treasury and Labour MP for Hampstead and Highgate, north London, is under investigation for the late registration of interests, according to the Parliamentary Standards Commissioner's website.
It followed a Mail investigation into Ms Siddiq's failure to register income from a London rental property for more than a year. (Source: BBC and Daily Mail)
The investigation is understood to be related to Ms Siddiq's failure to report rental income from a London property, which a Labour spokeswoman described as 'an administrative blunder' for which she apologized.
The spokesman said: "Tulip would cooperate fully with us.
Ms Siddiq is the first MP of the new Parliament to be placed under investigation by the Standards Commissioner.
She previously apologised after breaking MP rules over her financial interests earlier this month.
Sir Keir Starmer has repeatedly vowed to beef up integrity in public life. The Prime Minister said this month: 'People falling short of the required standards will face consequences, as you would expect.'
A spokesman for Labour said: 'This was an administrative oversight which was declared with the Commons registrar and Tulip apologised as soon as she was made aware of the issue.'
Last year the Commissioner put MPs on notice over late registration of interests, telling them it 'undermines the registration system. Members are personally responsible for timely registration. Future breaches will be investigated and reported for sanction.'
Investigations into three former MPs which began during the last Parliament remain open.
Former Conservative MP Bob Stewart is being investigated for failing to declare an interest and an alleged lack of co-operation with the watchdog's inquiry.
Ex-Tory and Reclaim MP Andrew Bridgen is being investigated over registration of his interests, while former Tory Sir Conor Burns is being investigated for use of information received in confidence.
During the last Parliament, the Standards Commissioner opened more than 100 investigations into MPs, the majority of which were resolved by 'rectification' - a procedure that allows MPs to correct minor or inadvertent breaches of Commons rules.
Tulip, the candidate of Labour Party, has won from London's Hamstead and Highgate constituencies for the fourth time in a row in last election. She got 23432 votes in this seat. Her nearest rival, Don Williams of the Conservative Party, got only 8462 votes.
The 41-year-old Tulip is seen by political observers as one of the most promising politicians of the new generation within the Labour Party. In the 2015 election, Tulip won the Labour Party's non-safe seat for the first time in a fiercely contested seat.