Two hospitals in the London area are the first in the UK to go live with e-booking systems under the government's £2.3bn national programme for IT (NPfIT) in the NHS.
A third hospital, Mayday Hospital in Croydon, was due to go live between April and June, but said it has hit delays because of problems involving links to its patient administration system.
The NPfIT, which is due to become an executive agency of the Department of Health next year, told Computer Weekly it could not divulge the names of the "early-adopter" hospitals.
An NPfIT spokesman said this was because "we intend to allow these early adopter sites to undertake their work uninterrupted".
He added, "It would be unfair to submit them to the attention of the media."
But a spreadsheet of early-adopter sites has been leaked to this magazine. It showed that Mayday, Whittington and North Middlesex University hospitals were due to go live between April and June with systems that will allow GPs to book hospital appointments electronically.
In fact, Whittington and North Middlesex went live in July.
A spokeswoman for the two London area sites which have gone live told Computer Weekly they were hoping to have a "big launch" announcement.
The two hospitals have booked six or fewer patients since the scheme went live, said the spokeswoman.
An NPfIT spokesman said, "The Choose and Book system is only currently available to a handful of GPs booking into a limited number of hospital specialities and so only a small number of bookings have been attempted so far. All have been successfully conducted.
"At this stage of the implementation we always intended to focus on making the system work rather than on volume. This is to set a firm foundation ready for a subsequent ramp up in volumes," the spokesman said.
NHS IT: the unanswered questions >>
Ins and outs of Choose and Book
Electronic booking systems - called Choose and Book - are designed to give GPs a way of shopping around for the earliest appointment for a patient.
In a policy document issued two weeks ago to trust chief executives, the Department of Health said that, from August under the Choose and Book scheme, patients waiting more than six months for elective surgery "will be offered faster treatment at an alternative hospital".
Choose and Book systems were due to have gone live in June. The government's target is for all patients to be able to book appointments from a choice of four or five hospitals by 2005.
Trust IT directors warn of risks
IT directors in trusts across England are recommending their boards approve business cases for implementing new national systems locally, but are also warning of risks of failure or uncertainties.
Stuart Threlfall, director of IT and service modernisation for King's Lynn and Wisbech Hospitals NHS trust, referred in a board paper dated 26 July to a "significant and unacceptable gap in funding".
He said the gap between the available funds and the expected cost of the systems has been reduced, but that there was still a gap. A spokesman said it was not always possible to provide answers to very specific and detailed questions.
"However, there will be greater clarity as the NPfIT develops and as local plans are taken to a lower level of detail."