Thug jailed after pushing pensioner off a bus Derek Thomson handed three years after leaving pensioner in a coma He shoved retired Royal Navy seaman Frederick Fenn off a bus When Mr Fenn struck his head it was like a 'water melon hitting concrete' Caged: Derek Thomson is behind bars after his sickening attack left a pensioner in a coma A thug who shoved a pensioner off a bus, causing him to smash his head on the pavement which left him in a coma lasting several weeks, has been jailed. Derek Thomson, 27, attacked retired Royal Navy seaman Frederick Fenn, 67, following a row between the pair on a bus in Ipswich. When Thomson bundled his victim into the street, the sound of Mr Fenn's head colliding with the ground was described in court as like 'a water melon hitting concrete'. Thomson had denied grievous bodily harm, but the Ipswich man was found guilty and jailed for three years yesterday at Ipswich Crown Court. During the trial, the jury had been told that Mr Fenn sustained 'life-changing' injuries when he was set upon by Thomson during the brutal assault last December. He was described as 'independent, confident and active' but since the attack had been completely different and appeared to relatives to be 'removed from reality'. Mr Fenn, who had also served in the Merchant Navy, spent several weeks in a coma at Addenbrooke's Hospital in Cambridge, before he regained consciousness and was moved to Ipswich Hospital. The pensioner had been out for lunch on the day of the attack, and was returning to his Ipswich home by bus at about 6pm when trouble flared. Bus driver Jonathan Bethell said Mr Fenn had initially got off the bus, but had then got back on again. He explained Mr Fenn was then bundled backwards off his bus, which was at a standstill, by a man. He added: 'He pushed him backwards out of the open door of the bus.' Mr Bethell described the horrible sound of Mr Fenn's head hitting the ground as like 'a water melon hitting concrete'. Thomson claimed in court he had been acting in self defence and had not deliberately pushed Mr Fenn off the bus. But defending Thomson, Ian Duckworth said his client accepted he was going to prison after being found guilty. Shocking: Defoe Road in Ipswich, the scene of the assault that left Frederick Fenn with life-changing injuries