Mistake of fact does not invalidate a search warrant

The decision offers continued support to officers when applying for search warrants

R (on the application of Amber Daly) v Commissioner of Police of the Metropolis and another Divisional Court (Sir Brian Leveson (President Queens’s Bench Division) and Males J)

Executive summary

A mistake of fact does not invalidate a search warrant if otherwise this would defeat the purpose of search warrants by invalidating all warrants that failed to unearth evidence sought.

Background and facts

Thermal images obtained by a police camera suggested that a significantly greater amount of heat was being emitted from the roof of 109 Marsala Road, London. Excessive heat is associated with the use of hydroponic lighting in the cultivation of cannabis plants. Based on this evidence a search warrant pursuant to section 23 of the Misuse of Drugs Act 1971 was granted by South East London Magistrates’ Court on 12 December 2016.
On 15 December 2016 a number of police officers forced entry pursuant to the warrant and handcuffed and detained the claimant, Ms Daly, who was on the premises. The search proved negative. The claimant sought to judicially review the decision of the Magistrates’ Court to grant the warrant.


The claimant alleged that there had been a mistake as to fact and that the application was malicious. Her expert propounded that the colour of the roof on the images obtained (black) suggested an absence of heat, but contrary evidence for the police was to the effect that an infra-red camera at night would indeed depict hot areas as black. Other evidence suggested the source of excessive heat was a new boiler installed at the premises and put on full power to dry out renovation work.

The court was not persuaded that a mistake as to fact, even if one had been proved, was sufficient to establish a claim. To hold otherwise would remove the potency of search warrants whenever an authorised search did not lead to the discovery of evidence and remove the protection that warrants give officers when they have reasonable grounds to secure the grant of a warrant. 

Although it was established that mistake as to fact could in some circumstances give grounds for judicial review, Sweeney J had observed that this should not normally be allowed in the context of criminal proceedings for the fear of opening the floodgates - R (Director of Public Prosecutions) v Sunderland Magistrates Court [2018] EWHC 229

The case of Gibbs v Rea [1998] AC 786 established that a search warrant could be challenged on grounds of malice but the court rejected such a claim in the circumstances of this claim. The application was dismissed.


The decision offers continued support to officers when applying for search warrants and acting in accordance with such authority when carrying out searches. The floodgates would indeed be opened if challenges could be mounted every time a search failed to turn up evidence. 
There remain suitable and stringent safeguards governing applications for and the grant of search warrants. For a useful reminder, readers are referred to Weightmans’ legal update on the decided case of R (on the application of Mills) v Sussex Police (2014) EWHC 2523, cited to the court in this case.

If you would like any further information, or have any questions, please contact our partner, John Riddell, on 0116 242 8925 or john.riddell@weightmans.com.

Share on Twitter