Shares in Carlton and Granada, the joint backers of ONdigital, fell on rumours that only 43 per cent of homes would have access to a full service at the launch of the operation.
Shares in Carlton closed off 5 per cent at 403p as the speculation grew that there may be problems with the launch. Granada fell 2 per cent to 886p.
The share price fall was triggered by research sent to institutions yesterday that concluded: "ONdigital will be able to provide a full service to 43 per cent of households, compared to BSkyB's 100 per cent national coverage."
The research was published under the name of Claritas, a little-known consumer research group. Data for the research was supplied by the Independent Television Commission.
Carlton and Granada denied there were any problems with set-top boxes, due to go on sale on Sunday, and claimed rival companies were deliberately spreading disinformation.
Andrew Marre, spokesman for ONdigital, said: "Everything is going fine with the launch. This speculation is simply not true." He added that the company expected to give coverage to 70 per cent of households this year and 90 per cent next year. Ondigital pointed to surveys published by trade magazines which showed that Sky's coverage was less than 100 per cent.
A spokesman for Carlton said: "ONdigital is going to be on air, on time." A press launch for the set-top boxes will take place today and boxes will be on sale on Sunday, he added.
Analysts yesterday raised concerns that ONdigital may have failed to generate enough public interest. One said: "If they are launching in four days' time, their marketing has been pretty low key."
Granada hinted that the rumours originated with arch-rival Sky Digital and had no substance. "All these rumours are being chucked into the market and there has been no truth in them," the spokesman said.
A Sky spokesman denied any smear campaign. "We have gone out of our way to say we are not going to respond to any of these suggestions of problems with our competitors."