Providers say delays in detailed government proposals for "CAT-marked" ISAs - savings meeting prescribed criteria for Cost, Access and Terms - mean few, if any, of the products will be available to the public on schedule.
Hard proposals have been put back until October at the earliest following the last cabinet reshuffle, when Helen Liddell, the Treasury minister in charge of the plans, was replaced by Patricia Hewitt.
Autif, the unit trust trade body, now says it is going to be "impossible" for its members to adapt computer systems in time to offer unit trusts within CAT-marked ISAs by 6 April, the scheduled start date.
Philip Warland, its director-general, said unit trust firms - already preoccupied with screening for the millennium computer bug - had "not the faintest prayer" of having systems ready.
M&G, one of the biggest unit trust managers, said Treasury plans for single pricing on CAT-marked ISAs would add to systems problems. Most unit trust providers are still not set up to offer single-pricing on unit trusts.
The Government's initial plans for CAT-marking have irritated many fund managers because of a plan to give the Treasury seal of approval only to unit trusts which track an index of leading shares. Several leading industry figures - including members of the Personal Investment Authority, the personal finance watchdog - have warned of a potential "mis-buying" problem.
They say the Government could be blamed if customers lose money in products holding the Treasury's seal of approval.
While the delays are certain to affect ISAs carrying the Government's CAT-mark, many providers will offer ISAs which are not endorsed by the Treasury.