Lord Carlile has told BBC Radio 4's Today programme that yesterday's terrorist attack in London was, in effect, made easier by a paint-only cycle lane on Westminister Bridge.
Lord Carlile is a crossbench peer and, from 2001 to 2011, he was the government's independent reviewer of terrorism legislation.
Speaking on the news programme at 7am from a radio car on the bridge he said the driver of the 4x4 which mounted the footway and killed pedestrians walking along the bridge had "uninterrupted" access to the footway because of a cycle lane. The attacker then abandoned his car and fatally stabbed PC Keith Palmer, a policeman guarding the Houses of Parliament.
Lord Carlile said parliament was "barely penetrated" but that "there may have to be changes in the way we protect parliament and other major buildings."
He added: "We may have to look at the new traffic arrangements around Westminster, which have changed in the last few months and opened up a wide new cycle lane along which this vehicle travelled uninterrupted."
The parliamentary estate is ringed by public highways, including roads, footways and a small length of kerb-protected cycleway. However, the cycle lane on Westminster Bridge is protected by paint alone, although work is soon to start on adding kerbs to the cycle lane.
The interview can be heard on the Today programme's website at 53 minutes 30 seconds.
Later in the programme a presenter asked London Mayor Sadiq Khan about easy access to the cycle lane, but Khan did not respond to that point.
Former mayoral candidate Christian Wolmar said Lord Carlile's remark was an example of "extraordinary hostility to cyclists." He asked, "how can Lord Carlile think Westminster Bridge cycle lane made it easier to attack? Quite the opposite."
The spot where the British-born attacker abandoned the 4x4 is just beyond the bridge and where the protected cycleway starts. It is also about 30 metres from where, in December last year, transport minister Chris Grayling "doored" a cyclist. Some MPs and peers blame London's cycleways for, among other things, congestion and air pollution. In 2015, Lord Lawson claimed that cycleways were more damaging to London than anything since the Blitz.