A Cambridge University academic will warn Members of Parliament that the increasing collection of electronic data such as CCTV pictures is creating inequalities in legal cases.
Ross Anderson, professor of security engineering, will issue the warning as he gives evidence to the Commons home affairs committee's inquiry into the "surveillance society" today.
Speaking ahead of his appearance, Professor Anderson said: "Surveillance creates an inequality of arms in both civil and criminal cases. The police can easily get CCTV or ANPR [automatic number plate recognition] data to show you committed a crime, but you have great difficulty getting this data to establish an alibi."
The academic, who is also chair of the Foundation for Information Policy Research, added: "A bank can get CCTV data to prove you made a disputed ATM transaction, but you can't get this data to prove that you didn't."
Last week, the committee heard evidence from Nick Eland, legal services manager of Tesco, about how the supermarket giant uses the data it collects on customers and from Martin Briggs, corporate affairs director of LMG, the firm behind the Nectar loyalty cards.
Information commissioner, Richard Thomas, has also appeared before the inquiry, where he called for his office to be given new powers allowing uninvited investigations to examine data protection measures.