The opening date of England's biggest single site independent sector treatment centre is still uncertain - amid signs that the potential financial impact on local NHS bodies is causing concern.

The Nottingham ISTC will handle 24,000 day-case procedures and 160,000 outpatient appointments a year. Staff from Nottingham University Hospitals trust, which runs the adjoining Queen's Medical Centre, are due to be seconded to the centre and the hospital will also provide some support services.

But the opening of the centre, originally expected at the end of last year, was postponed until March and has now been delayed again with no date announced for the opening.

The centre is to be run by Nations Healthcare, now part of Circle Group. A Nations spokeswoman said it hoped to announce a date for the opening of the centre shortly and the delay was to ensure it "best meets the needs of patients".

Nottingham City primary care trust was told at the end of March that the mix of cases to be treated at the centre was under discussion and would be agreed by the end of May.

Board members also heard that an "independent review of the financial positions presented by each party" had been commissioned.

The centre was originally expected to be cost-neutral for the hospital trust, with the loss of income from its activity being offset by payments for staff working there.

The trust's audit committee was told the offset between lost income and reimbursement for staff and services could no longer be guaranteed, mainly because the case-mix of work transferring was changing.

Finance and procurement director Mike Mansfield said this was a "financial challenge" for the trust.