Bomb disposal experts carried out a series of controlled blasts in the western English town of Cheltenham, media reports said Saturday, after police evacuated the area and held two men on terror charges.
The local men, aged 52 and 31, were arrested over explosives offences in Friday raids on two locations in a quiet residential suburb of the spa town, which is also home to Britain's national electronic surveillance centre.
Some 100 homes were evacuated overnight as counter-terror police investigated "items found in a garage" and the pair were then rearrested on suspicion of preparing or instigating a terrorist act, police said.
Police warned residents to expect a "controlled disruption" at the site, where four loud blasts were heard in television footage broadcast by ITV on Saturday afternoon.
Britain's government communications headquarters, GCHQ, is based in Cheltenham, where thousands of workers gather intelligence through intercepting electronic communications.
Mainly based in a purpose-built development known as the "doughnut", they also defend the country's own information and communications systems from hackers.