David Miranda, the partner of Guardian journalist Glenn Greenwald, is taking legal action against the British government after he was detained and searched at Heathrow airport over the weekend, his lawyers said Tuesday.

Miranda argues it was illegal for police to seize data from him and wants to ensure that they do not do anything with the material until a judge has heard his claim.

“We are most concerned about the unlawful way in which these powers were used and the chilling effect this will have on freedom of expression,” said Kate Goold, of the law firm Bindmans, which is representing Miranda.