The Welsh Tourist Board, which runs the accreditation scheme in conjunction with the Sports Council for Wales, said the two centres could not be named because confidentiality was guaranteed to those taking part.
A spokeswoman for the WTB said, "It is a weakness of the voluntary scheme. There is also the problem that an awful lot of centres don't take part. All we can do is try to get the message across that it is in activity centres' own interest."
Both the WTB and the Sports Council for Wales are backing calls for statutory inspections of activities centres. Such demands intensified followed the Lyme Bay canoeing tragedy in March last year when four sixth-formers died on a school activity break.
The WTB pioneered its independent inspection scheme which has operated since January 1993. As well as independent inspections there is a code of conduct. The bonus for centres taking part is that they are included in promotions and marketing drives by the tourist board. They also feature in a brochure produced each year.
But the spokeswoman admitted that only around 130 of the 500 activity centres in Wales take part. Because there are no statutory regulations governing the industry there is nothing to prevent centres which fail to receive accreditation from continuing to operate.
She said, "It is a matter not of punishing centres that fail, but of helping and advising them to meet higher standards. We hope schools planning outdoor activities in Wales will look to our approved list of centres . . . We recognise the drawbacks with our scheme but we think this is the best we can achieve."
A House of Commons committee is currently conducting an inquiry into the safety of children using outdoor activity centres. The inquiry will question whether there is adequate supervision for pupils visiting outdoor centres and examine steps being taken to improve safety. These include an inspection programme by the Health and Safety Executive, the guidance recently issued by the Department for Education and the self-regulatory code of practice produced by the Activity Centres Advisory Committee.