Four people have been arrested on suspicion of "failing to disclose information which might be of assistance in securing the apprehension, prosecution or conviction of a person involved in an act of terrorism".
Two men, aged 21 and 31, and a 25-year-old woman were arrested by counter-terrorism officers at two residential addresses in east London, and a 25-year-old man was arrested at a residential address in Lancashire, Scotland Yard said.
The arrests come after two brothers who were stopped by police in Dover appeared in court last month accused of travelling to a terrorist training camp in Syria.
More top news
The father-of-four from Cardiff with appear in court this afternoon charged with terrorism-related murder and attempted murder.
Industrial vacuum cleaners and magnetic wands will be used each night during the summer to remove metal particles, dust, oil and grease.
Detective Superintendent Fiona McCormack said the Hotpoint FF175BP model had not been subject to any product recall.