Former Labour minister Stephen Timms is in hospital after being stabbed.
Police said Mr Timms, 54, was stabbed in the stomach at a constituency event in Newham, east London, but stressed his injuries were not life-threatening.
A 21-year old woman has been arrested after the attack at about 1500 BST but police have not given further details about what happened.
Mr Timms served at the Treasury under Tony Blair and Gordon Brown and was recently re-elected as MP for East Ham.
The MP is reported to be sitting up in Royal London Hospital and talking to staff.
Largest majority
He was stabbed at the Beckton Globe Library, where he holds a regular constituency surgery.
Mr Timms was a close confidant of both Gordon Brown and Alastair Darling during Labour’s 13 years in government, serving latterly as financial secretary to the Treasury.
He has been MP for the constituency – and previously for Newham North East – since 1994.
His personal popularity in his constituency is reflected by the fact that he secured a 7.7% swing from the Conservatives in last week’s election, when Labour was generally losing ground across the country.
Mr Timms won a remarkable 70.4% of the vote and his 27,826 majority is the largest in the new House of Commons.
Married to Hui-Leng Lim, he describes himself as a Christian Socialist and is Labour’s vice-chairman for faith groups.
Cabinet ministers and former ministers, particularly those who served in departments such as the Home Office and the Northern Ireland Office, have security protection; the majority of MPs do not.
In 2000 Liberal Democrat MP Nigel Jones was wounded and his aide, Andrew Pennington, was stabbed to death in a frenzied sword attack during a constituency surgery at the party’s office in Cheltenham, Gloucestershire.
Mr Jones, a married father of three, was conducting his weekly surgery when he received lacerations to his hands and arms while fending off blows from Robert Ashman, who was jailed for manslaughter and attempted murder.
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