The government is expected to rewrite its guidance on implementing cancer czar Mike Richards' recommendations for top-up payments.
Trusts have been observing the draft guidance since it was published in November.
As it stands, primary care trusts face increased bureaucracy as an unintended consequence.
Cancer clinicians are already expanding the number of requests for exceptional funding sent to PCTs to include "clinically non-exceptional cases".
Traditionally, the exception route was only open to patients with recognised criteria such as an unusual health need where no commissioning policy was in place.
But in a move likely to be followed by other trusts, Mark Wright, Royal Marsden Foundation trust's head of contracts, has written to commissioners saying the trust must now send exceptional case requests even where the patient does not meet exception criteria.
Exhaust all routes
This is to fulfil the requirement to "exhaust" all NHS funding routes before allowing private treatment.
"While the trust does not want to compromise the quality of the existing [exceptional circumstance] process, it is unavoidable that clinically non-exceptional cases may need to be submitted under this guidance," the letter says.
The DH said the line in the guidance about exhausting all reasonable avenues for securing NHS funding was "an important safeguard for patients", but revised guidance, which took into account consultation responses, would be published shortly.
A spokeswoman said: "There is no intention to require clinicians to use exceptional funding procedures where this would be clearly inappropriate."
National clinical director for cancer Mike Richards told HSJ: "During the consultation, comments have been made about this particular point and clearly the DH is now considering that in drawing up the final guidance."
PCT CONCERN OVER CONSTITUTION
Measures in the NHS Constitution to increase transparency will allow patients and their legal teams to crawl over primary care trust decisions and seek judicial review.
Lawyers have raised concerns over the duty for PCTs to demonstrate they followed internal processes to the letter and set out clear reasons when making decisions. The constitution even reminds patients they can seek a judicial review if they believe the NHS has acted unlawfully.
There is also a risk that, as well as patients and lawyers attending exceptional case panel hearings and challenging results, drug companies and patient groups could send round robin letters to PCTs demanding to know their reasons for all funding decisions, before targeting legal action on PCTs with weaker rationales.
Inconsistent decision making
Commissioners fear the twin threats will exacerbate inconsistent decision making.
UK Public Health Commissioning Network chair Daphne Austin said: "Where it breaks down is whether or not [PCTs] can hold their commissioning position… Some PCTs find it hard to say no to patients coming to the individual funding request panel even though it is obvious the patient is not an exception.
"The minute one PCT says yes, the next one gets pressure."
The DH said the constitution was a "declaratory document" and had not been set out in primary legislation, in order to avoid it becoming a lawyers' charter.