A gang of nine men targeted elderly victims by pretending to be police officers in a fraud worth nearly £330,000.
The scam involved calling people, impersonating police, and telling them that they were investigating fraudulent activity on their bank accounts.
They would then ask the victims to withdraw large sums of money, convincing them it was part of the investigation, before either sending a "courier" to collect the cash or transferring the money to the account of a "financial mule".
Between March 1 2016 and November 29 2016, the gang were able to run the scam 34 times, earning them £215,641 and a further £122,445 in unsuccessful attempts, totalling £328,086.
The gang members would predominantly target areas in London and Hertfordshire, including Harrow and the majority of their victims were elderly.
The phone scams were also carried out in Surrey, Kent, Bedfordshire, Nottinghamshire, Yorkshire and the Thames Valley area.
Hertfordshire Constabulary investigated reports of the scams, processing a number of warrants which were executed in November 2016.
The raids led to charges being brought against nine members of the gang, six of whom were charged with conspiracy to commit fraud, with the three others charged with money laundering.
The men were all found guilty following a five-week trial at St Alban's Crown Court on August 7.
On Friday (September 21), six members of the gang were sentenced to a total of 27 and a half years in prison, while three were given suspended sentences.
Sheikh Hussain of Great Russell Street, Nahid Uddin of Charlton Street and Mohammed Abdul Khaled of Portpool Lane, all aged 24, were sentenced to four years in prison
Masum Uddin, 23, of Orde Hall Street was handed a seven-year prison sentence.
Mohammed Abdulahi, 22 of Cumberland Market was sentenced to six years and six months imprisonment, for acting as a courier to collect the fraudulently obtained cash from elderly victims.
Fellow courier Mushahid Miah, 24, of Ampthill Square, was sentenced to two years in prison.
Dedar Ali, aged 24, of Cressfield Close was handed a six-month suspended prison sentence for money laundering.
Abdul Basit Khan, 26 of Calverton Road, Luton, and Abdalla Abdalla, 27, of Piper Close, both received the same suspended sentence, but were also ordered to carry out 120 hours unpaid work.
Detective Constable Julian Griffiths, from Hertfordshire Constabulary’s Serious Fraud and Cyber Unit said: “These men callously targeted elderly and vulnerable victims and defrauded them out of their life savings.
“I am pleased that they are now behind bars and I hope it brings some small comfort to the victims and their families who have been left devastated by the actions of these men.
“We have done a lot of work to raise awareness of these scams but we need people to continue spreading the word to friends, relatives and neighbours to help prevent more people falling victim to them.
“Please remember that the police and banks would never ask for your PIN over the phone and would never ask you to withdraw cash and hand it to a courier.
"If you receive a call you are suspicious of, please hang up and alert the police.
"Remember to wait at least five minutes, or use a mobile phone to ensure you aren’t reconnected to the offender.”