David Miranda's lawyers have written to Home Secretary Theresa May and Met Police Commissioner Bernard Hogan-Howe to express concern about his "unlawful" detention.
Criminal lawyer Kate Goold of Bindmans LLP said: "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."
The independent reviewer of terrorism legislation said he will examine the detention of David Miranda at Heathrow Airport.
Nick Clegg has backed David Cameron's decision to send a top civil servant to The Guardian to urge them to destroy classified data.
The Guardian journalist whose partner was held at Heathrow Airport hits out at the UK as he gives ITV News his first British TV interview.