Coun Carl Macey, chair of the health scrutiny panel for Lincolnshire, last month wrote to Lincolnshire West Clinical Commissioning Group to express concerns over poor performance of the patient transport service.
He said he felt “no confidence” in the service and called on officials to exit from the contract.
The CCG recognised that the company had an “unacceptable level of performance” in recent months,.
But Tim Fowler, director of commissioning at Lincolnshire West CCG, said in a report that moving to another provider would be a risk.
“LWCCG will continue to work to address the concerns raised by the committee regarding Thames’ continued unacceptable performance,” he said.
“Currently it is the view of the CCG that there is an unacceptable level of risk of giving notice to exit the contract and moving to a new provider at this time
“The CCG will update its assessments of risk associated with the Thames contract in light of changing circumstances and new information and in the absence of significant improvement may give notice at a future date.”
It comes after Thames showed a drop in performance against key indicators at a meeting of the health scrutiny panel in December 2018.
Mike Casey, general manager of Thames, assured councillors that “there was still much more to do” and that the service was on a “difficult journey”.
Officials from the CCG will give an update on the contract to the Health Scrutiny Panel for Lincolnshire on January 23.
Lincolnshire West CCG, which is the lead commissioner for non-emergency patient transport services in the county, contracted the company in July 2017.
The service came under criticism from patients and forced Thames to apologise in February 2018 for poor performance in the county.
Since then, the firm has undergone a management restructure which includes Derek Laird, former commercial director of West Midlands Ambulance Service, taking over as chief executive.
Despite the improvement in performance, Thames recently lost the contract for non-emergency patient transport in the north of the county.