NHS guidelines prevent trusts from "actively recruiting" from developing countries who are battling to prevent a damaging brain drain.
But Liberal Democrat health spokesman Paul Burstow said new research showed overseas nurses from developing countries such as the West Indies and South Africa were being recruited by the "backdoor".
Private nursing agencies are not covered by the guidelines and the Liberal Democrats insist many nurses from developing countries subsequently end up in NHS hospitals.
They are calling for a "kite mark" for nursing agencies following NHS guidelines and not actively recruiting from developing countries experiencing acute nursing shortages.
But the Department of Health maintains it is drawing up a new code of practice that will cover agencies.
Increasing numbers
The UK Central Council for Nursing, Midwifery and Health Visiting said the registration figures for March 1999-2000 showed an increase of 63% on the previous year in registrations from the West Indies and 127% from South Africa.
By far the largest foreign contingent of nurses in the UK are from the Philipines, which is said to train more nurses that it can employ and provides about 47% of the UK's foreign nurses.
The UKCC registered 13,750 Filipino nurses up to March 2001, an increase of more than 1,400% on those entering in the year up to March 1999.
Dee Borley, director of the Royal College of Nursing's advice line Nurseline, said the mobility of nurses did benefit patients.
But she insisted: "The Department of Health guidance that trusts should not target recruitment drives at countries with their own nursing shortages is clear.
'Blind eye'
"Individual nurses have the right to travel and work overseas to develop their experience and further their careers and many black nurses in South Africa were denied this opportunity under apartheid."
Mr Burstow said: "It is a scandal that the NHS is turning a blind eye to the rising numbers of agency nurses coming from developing countries.
"The damage this brain drain does to the health care systems of third world countries is unacceptable."
Mr Burstow will use an adjournment debate in the House of Commons at 2230BST on Monday to discuss the matter.
'Serious concern'
A spokesman for the Department of Health insisted the NHS did not recruit from developing countries and worked to prevent any active recruitment.
But he admitted: "We do recognise that further steps are needed. It is a cause of serious concern that some commercial agencies appear to have targeted developing countries for international recruitment.
"We will soon publish a new code of practice which reinforces our policy that international recruitment must never be carried out against the interests of host countries.
"Commercial recruitment organisations played an active part in its preparation, and for the first time it will apply to their work also. Trusts will not be allowed to use those agencies who do not comply with the code of practice."