Andrew Hennells , pictured , posted a message on Facebook admitting his plans to rob a Tesco supermarket 15 minutes before holding up staff . A man who boasted about plans for an armed robbery on Facebook minutes before he threatened staff in Tesco has been jailed for four years . Andrew Hennells posted details of his plan to the social networking site - stating he was 'Doing . Tesco . Over ' at 7.25pm on February 13 . A quarter of an hour later , Norfolk Police were alerted by a member of the public to a man brandishing a knife demanding cash from staff working at the supermarket giant 's King 's Lynn branch . Hennells fled the scene before police arrived , but he was quickly arrested in a nearby pub with £410 in stolen cash . Norfolk Crown Court heard that officers also recovered a knife . Last month , the 31-year-old , of Gaywood , King 's Lynn , admitted robbery and carrying a knife as an offence . Sentencing him to four years in prison for armed robbery today , judge Anthony Bate said Hennells posed a 'high risk of serious harm to the public ' . The court heard how armed police were deployed after the alarm was raised . Hennells had escaped after stealing a car belonging to a retired couple who had stopped to use a cashpoint . But officers tracked him down in a nearby pub , finding him carrying a knife and £410 in stolen cash . Another count of robbery relating to the car-jacking was left to lie on file , Norfolk Police said . Outside court , Sgt Pete Jessop , from King 's Lynn CID , said that the Facebook confession made it easier to prove the case . Hennells posted this message only 15 minutes before threatening staff at Tesco 's in King 's Lynn . A member of the public alerted police to a man threatening a member of staff in the store ( pictured ) Hennells , 31 , was then found by police in a nearby pub , with £410 in cash on his person . Speaking after the first hearing , Sgt Jessop had said : 'We have not got to the bottom of why he posted the pictures and words on Facebook , or why he did the job in the first place . 'It was bizarre and an unusual set of circumstances . 'While the message and pictures on Facebook did not solve the case , it did confirm what we already knew . Hennells held up staff at the Tesco store in King 's Lynn , pictured on Friday , February 13 . 'But the thing that made it easier and quicker for us to solve the case was the assistance from the public . 'However , the quickness does not take away from its seriousness or how traumatic it was for the victims of the robbery . ' Hennells made a series of other posts to Facebook in the hours before the robbery , including a picture of a large knife , and sharing a Bare Knuckles Gypsies ' 'The hardest man in Ireland ' video .
Andrew Hennells threatened staff in Tesco with a knife of February 13 . Fifteen minutes before the raid he posted details of his plan on Norfolk Crown Court . Facebook judge deems 31-year-old 'high risk ' to the public .