Smith, also a director of data protection law consultancy Opt-4, said that the market would "change dramatically" if all businesses had to obtain permission before contacting new or current customers.
Phorm is designed to tailor ads to individuals by looking at their web browsing history and taking account of the sites they visit and search terms they use.
Earlier this month, the ICO made the controversial decision to stop Phorm from automatically assuming permission from web users and has insisted it gets all users to enroll before it tracks their online movements.
Speaking at the IDMF, Smith said: "Companies would lose around 80% of their customer data if the government imposed mandatory opt-in regulations and it could put a lot of companies out of business." She was not overly concerned by the recent ICO decision however, assuring that the DM industry could avoid future legislation.
"If we stay sensible and maintain standards then we can avoid a mandatory opt-in. It's only when companies don't meet targets or don't follow the rules that we are put under pressure by lobbyists."
Since an opt-out service was introduced on the electoral register, numbers of people choosing not to receive any marketing information from businesses has increased to 40%. Telephone is the most opted-out medium with 14.7 million people registered on the Telephone Preference Service.