Patients have had to be re-admitted into NGH because of delays by a non-emergency ambulance service.
Private company NSL Ltd is paid by the NHS to take patients to scheduled hospital appointments and bring them home again.
But a number of its ambulances have been so late that patients well and ready to leave have had to be sent back to already busy wards.
NGH board papers say: “NSL were unable to deliver transport for patients within the allotted time.
“The trust deemed that the delayed arrival time of the transport was too late for patient to be moved, so patients were re-bedded.”
The issue is such an important one because the speed and smoothness of discharging patients are the biggest factors in helping A&E run properly.
People can only be admitted to beds if fit patients leave.
In December, 22 patients had to be readmitted and the number by the end of January is predicted to be 30.
NGH chief executive Dr Sonia Swart wrote to NSL - which is not expected to bid again for the contract when it runs out next March - expressing her concern.
The NHS has also issued the company with a warning.
NSL Ltd took over the non-emergency ambulance service from the NHS in July 2012.
But negative headlines have included elderly patients waiting up to 12 hours, the closure of its Northampton control room, and attempts by the company to alter the contract, which it had claimed was ‘unsustainable’.
The company is understood to have told staff it is not interested in winning any new patient transport contracts, which effectively means it will stop taking Northamptonshire patients after March 2017.