Last week Southwark Council's Healthy Communities Scrutiny Commission heard evidence from representatives of the NHS Southwark Clinical Commissioning Group in the wake of the critical report on Nexus published last month.
Two members of the commission who are also Nexus patients related their own experiences.
Cllr Maria Linforth-Hall praised the "fantastic, caring, great" staff at the Princess Street surgery but complained of administrative failings since the Nexus merger and noted that the clinic operates in "inadequate" premises for the growing local population.
"Without better premises, they will not be able to succeed," she said.
"The doctors are fantastic, the nurses are fantastic, but they just can't cope with the number of people on their books."
Cllr David Noakes, a patient at Nexus's Decima Street site, said: "I'm not very surprised as a patient that they have been put in special measures... I would agree with my colleague that since the merger the service has got worse."
Nexus provides GP services to more than 70,000 North Southwark residents from eight locations.
Last November CQC inspectors found more than 1,000 test results dating back to July 2018 "which had either not been filed or not been viewed and filed". 442 of these results were marked as being abnormal.
Dr Noel Baxter, clinical director for quality and service improvement at Southwark CCG, told the committee that Nexus had carefully followed up all the unprocessed test results identified by inspectors.
He said: "There is definitely risk of harm from systems not being in place ... but I would be very happy to assure you that patients have not been significantly harmed."