Under data protection law, firms must inform customers of the use of this type of technology. Most of the firms approached by the Telegraph said they do so in their privacy policies.
But Pat Walshe, of Privacy Matters, told the BBC: “Solely placing something in a privacy notice is not consent, and it is hardly transparent.
“The fact that tracking will take place and what that involves should be put in the user’s face and involve them opting in.
“The law is clear enough, what we need is regulatory enforcement. Just because this practice is widespread doesn’t mean it’s correct and acceptable.”
“Organisations must also use people’s information in a fair, transparent and secure way. “If anyone is concerned about how their data is being handled, they should contact the organisations first. If not satisfied, they can make a complaint to the ICO.”
British Airways, TalkTalk, Vodafone, Sainsbury’s, Tesco, HSBC, Marks & Spencer, Asos and Unilever and among the firms using such technology, according to the BBC.
The Telegraph contacted all of these firms. There is no suggestion that using email tracking technology is a breach of data protection law.
A spokesman for TalkTalk said: “As is common across our industry and others, we track the performance of different types of communications to understand what our customers prefer. We do not share this data externally.”
A British Airways spokesman said: “We take customer data extremely seriously, and use a cross-industry standard approach that allows us to understand how effective our customer communications are.”
Sainsbury’s and Tesco said they explain to customers what is involved in signing up for marketing emails in their privacy policies.