Patients are being forced to wait longer for hospital treatment in Harrow and the surrounding areas, figures show.
The number of people waiting to see consultants under the North West London Hospitals Trust has gone up in the past 12 months, according to the House of Commons Library.
But the trust has blamed a clerical error, saying the length of a patient's wait from referral from the GP was not being correctly counted.
However, others are not convinced about the glitch and are calling on the trust to take action.
Harrow West MP Gareth Thomas said: “These figures reflect the stories I have been hearing for some time from residents in Harrow.
“People are having to wait longer to get the treatment they need from our local hospitals.
“Sadly, they show yet again that David Cameron has broken his promise to keep waiting times low, and this is further proof that you can’t trust Tories with the NHS.”
The number of patients waiting for treatment went from 18,596 for December 2012 to 21,658, for December 2013, an increase of 16 per cent.
Last year, the hospital trust was ranked 145th out of 146 in a patient satisfaction survey.
Mr Thomas added: “There have been a severe cuts to social care in the area and I think that is putting a strain on our local NHS trust.
“I always welcome investment to the Northwick Park Hospital but I don’t think it will solve the problem.
“We need to make sure there is more investment in social care locally so patients are not left waiting.”
The trust said it had fully overhauled its systems to ensure the next batch of figures reflect an accurate waiting time.
The national target for patients to see a consultant within 18 weeks is 92 per cent, and in January 2014, the trust almost met the target by reaching 91.4 per cent.
Tina Benson, the trust's interim director of operations, said: “It is absolutely right and proper that patients are treated in accordance with government targets. We are committed to continuing to improve our performance on this measure as we improve our overall performance against 18 weeks.”