London (CNN) -- Nine men were jailed in London Thursday on terror charges, four of them over "an al Qaeda-inspired plot" to bomb the London Stock Exchange, UK police said.
Abdul Malik Miah, Gurukanth Desai, Shah Mohammed Lutfar Rahman and Mohammed Moksudur Rahman Chowdhury had pleaded guilty last week to the London Stock Exchange plot, police said.
Five others, Abdul Bosher Mohammed Shahjahan, Mohibur Rahman, Nazam Hussain, Omar Sharif Latif and Usman Khan, also admitted terror offenses, police said.
All nine were sentenced at Woolwich Crown Court Thursday to terms ranging from five to nearly 17 years, with some given indeterminate sentences with at least eight years to serve.
Deputy Assistant Commissioner Stuart Osborne, the senior national coordinator for counterterrorism, issued a statement saying: "This was one of the most significant and complex counter terrorism operations of recent years.
"We had a network of highly dangerous men based in three cities who were working together to plan terrorist attacks in the UK.
"Had we not taken action to disrupt this network, their actions could have resulted in serious casualties or fatalities."
Miah, who had previous convictions, was sentenced to 16 years and 10 months in jail, while Desai was jailed for 12 years, and Latif for 10 years and four months.
Shahjahan, Khan and Hussain were each handed an indeterminate sentence, with a minimum of eight years to serve. Mohibur Rahman was jailed for five years.
Chowdhury was sentenced to 13 years and eight months, and Shah Rahman to 12 years.
Osborne said a major covert operation had been put in place to monitor the suspects, who were based in London and Stoke-on-Trent in England and Cardiff in Wales.
At the height of the operation, over the 2010 Christmas period, nearly 1,000 police officers and staff were involved, he said in an online statement posted by West Midlands Police.
"These men were arrested when the balance between public safety and gathering evidence meant that we could not run the operation longer," Osborne said.
"This plot clearly demonstrates that there are still people living in our communities who are intent on doing us harm. If we are to find them and we are to stop them we must all remain vigilant and aware."
The investigation, which was coordinated by the West Midlands Counter Terrorism Unit, also involved police forces in London, Wales and Staffordshire, and national counterterrorism and security services.