"Until you get full guidance, I would go with the worst case scenario," he said.
However, he added: "But even if you do have an IHT liability, it doesn't mean [a DB to DC transfer] is a bad idea. The death benefit is often a lot better even with tax."
He said, while this ambiguity had been around for a long time, it had only become a hot topic since pension freedoms came in.
"We've probably been asked about it by advisers 10 or 15 times a week over the last year," he said.
He also pointed out that, even if the transfer was valued below the nil rate band, it would still use up the nil rate band, exposing the non-pension estate to IHT liabilities.
Mr Cameron said Prudential was in the process of asking HMRC for more clarity on this point.
HMRC confirmed that such transfers would be treated as chargeable lifetime transfers if the member died within two years of making the transfer.
However, a spokesperson said HMRC did not agree that the rules were ambiguous.
"The treatment of pensions and the IHT charges that may arise on transfers between pension schemes are explained in the IHT Manual (IHTM17000 onwards) and this information is also available on other websites and elsewhere so HMRC do not believe that there is no certainty on this point.
"HMRC are applying the legislation as set out in the guidance. There is no 'loophole' in the provisions; the treatment will depend on the member's circumstances," the spokesperson said.