DoH contract details revealed last week show it is currently negotiating with several private sector providers on a range of new ISTCs.
Future ISTCs include two centres run by Bupa in the North West and North East; three Netcare-run centres in the North West and East of England; and four in London, the East of England and the South East operated by Clinicenta a partnership between construction firm Carillion and a subsidiary of Australian private diagnostic firm I-Med.
The second-wave ISTC programme was originally anticipated to be worth£550m of private sector work for NHS patients per year, a figure now likely to be scaled back to£350m.
A DoH spokeswoman said: 'The number of actual ISTCs per scheme varies according to the service delivery model and scheme specifications.
'Contracts are yet to be announced for 15 elective schemes and five diagnostic schemes as part of phase two of the national programme.'
Last year the Commons health select committee published a critical report of the programme's first wave after it found no evidence of the value for money or heightened performance of ISTCs.
Committee chair Kevin Barron MP said it was 'ludicrous' that the government had made no attempt to make a systematic assessment of the ISTC programme (news, page 8, 27 July 2006).
In January a review by the Healthcare Commission said national data on the clinical quality of ISTCs was 'incomplete and of extremely poor quality'.