Monitor is “urgently reviewing” its expenses policy after its chair unwittingly ran up a bill of nearly £1,000 for short taxi rides in less than three months.

The regulator was invoiced £995.78 for 39 journeys taken by its interim chair Baroness Hanham, expenses documents reveal. All but one of the journeys were between the House of Lords in Westminster and Monitor’s Waterloo headquarters, just one mile apart.

Cab firm Addison Lee charged Monitor £24.75 a time for most of the journeys - made between January 22 and March 31 this year.

The 75-year-old Conservative peer, who joined the regulator in January, said she was “horrified” at how much her taxi rides had cost Monitor. She said in a statement: “Addison Lee is available to senior members of the organisation to ensure that they get to important meetings on time with as little disruption as possible and to enable them to work on their journey.

“However, I was horrified when I discovered how much my journeys to and from the House of Lords were costing the organisation. I have now stopped using Addison Lee and our finance team is urgently reviewing our expenses policy with a view to keeping the cost of taxis as low as possible.”

The sum per journey is around three times that quoted by other minicab companies.

The expenses document showed Monitor’s executive director of strategic communications Sue Meeson claimed £7.80 in expenses for a cab journey that was not on the Addison Lee account.

This journey was from Richmond House - two minutes walk from Parliament - to the regulator’s headquarters.

Monitor said in the last financial year it spent £15,000 on the Addison Lee contract and that individual users had not been aware of the cost of particular journeys at the time.

Addison Lee declined to comment.