"I was introverted as a boy and lacked confidence," he says. "I was certainly not academic. My goal from the age of 13 was to join the police force - I saw it as a mixture of Dixon of Dock Green, The Sweeney and Z Cars."
Never did he think he would go to university, let alone to Oxford and Cambridge. Yet Coatsworth has attended both: first Ruskin College, Oxford, where he did a year's course, and then St Edmund's College, Cambridge, where he has completed a three-year degree and written a dissertation on EU integration. Along the way he has overcome innumerable hurdles.
No one in his family had been to university. His father was a lorry driver and his mother a nurse. Moreover he had a speech impediment that was not addressed until he was seven-years-old. He failed the 11-plus and went to a secondary modern school. "I lived up to the low expectations that people had of me," he says.
How different has been the experience of his son, James, 21. In a neat piece of symmetry, James is completing his degree at the same time as his father, but he is graduating from Oxford University with a degree in politics, philosophy and economics. "I am really proud of my dad," he says. "I know how much work it takes and how difficult it is but I have been gearing up to this for 18 years whereas my dad hasn't."
Their story is perhaps a tale of two generations, 35 years apart. Father David, living in Kent, was the product of a selective system that divided children into grammar schools or secondary moderns. He was living at a time when aspirations were modest and far fewer young people went to university than do now. But he also has belatedly been a beneficiary of the special efforts that the ancient universities are making to give chances to people with the ability and motivation who missed out first time round.
By contrast, his son James came out of a Hampshire comprehensive, the Hurst community school. It was nothing special, he says. "It was your proverbial bog standard comprehensive and came about middle of the county for its GCSE results but it had some excellent teachers and fairly decent facilities. I was very happy there."
Crucially, the school was able to give opportunities to those who did well, and James did. At 16 he went to Queen Mary's College, Basingstoke, where he achieved two As and a B in his A-levels and notched up two AS levels. "I was always in the high sets and got fairly good grades," he says.
Back in the 1970s young David Coatsworth thought he was doing very well to be able to join the police force. You could enter in one of two ways - either by going in with five O-levels or by taking the police's entrance exam. Coatsworth chose the latter, and passed. Those were exciting times for a personable young copper with energy and ambition. "My police career was a wonderful education in the widest sense," he says. "I feel I have been a bit-part player in history."
Coatsworth was stationed in Cannon Row, which no longer exists, and spent time providing security for 10 Downing Street and the palaces. He remembers being at Downing Street the day that Margaret Thatcher went off to Buckingham Palace to inform the Queen that the Task Force was being sent to the South Atlantic. He also remembers Yvonne Fletcher, the woman police officer who was killed outside the Libyan Embassy in St James's Square.
One day he would be dealing with tramps under the arches at Charing Cross, the next helping tourists outside the House of Lords. From there he joined the CID and later, at the age of 21, became the youngest recruit to the Special Patrol Group. In 1981 he was to be seen on the streets of Brixton, dressed in helmet and riot shield, supporting the men in blue at the Brixton riot. "I was on page three of the Sun," he says. "The girls were moved off that day."
But suddenly, in 1988, Coatsworth's career in the Metropolitan Police was cut short. By then he was a member of the Territorial Support Group and was being driven at terrifying speed to an armed robbery. The car he was in crashed into a double-decker bus. Coatsworth suffered spinal injuries, head injuries and concussion. He was off work for 18 months, his marriage broke up and he was given a medical discharge. "It was tough, pretty desperate," he says.
It meant he had to rethink his career and, indeed, his life. He eventually found a job as firearms, weapons and pyrotechnics adviser to the BBC helping them with the guns they use in television productions. The high point was to appear in Pride and Prejudice with Colin Firth. It was fun but ultimately unsatisfying, although through the BBC he met his second wife.
So, he left for a job helping to get humanitarian aid to Bosnia and later worked at Olympia in Earls' Court. At this time he was asked to take a test by Mensa, and he got a high score. "I thought maybe I wasn't as dim as I thought," he says. "It gave me a boost."
Soon afterward, he saw a newspaper article about Ruskin College, Oxford. He got hold of a prospectus and, after reading it, decided it wasn't for him. But he was sufficiently interested to ring up. "I asked if there was someone I could speak to and was put on to this guy," he recalls. "We were on the phone for an hour. All the reasons I put up for not thinking I was suitable received the response 'Let us be the judge of that'."
He found out later that the man on the other end of the telephone was Ruskin's former principal, Jim Durcan. He persuaded Coatsworth to take a look at Ruskin. So, he signed up for an introductory weekend and decided to take the plunge.
His new wife supported him. Thus, at an age when most people are in mid-career, Coatsworth was learning about law, industrial economics, and employment studies. "It was absolutely fantastic," he says. "I loved studying. I also did a course on Marx and on music appreciation."
He was able to survive by drawing on his savings and through his wife's earnings. As the year wore on, one of his lecturers urged him to go on to university but Coatsworth wasn't very keen because he thought he wasn't academic enough. The Ruskin year enables students to move onto the second year of an Oxford Brookes degree. But Coatsworth was adamant, even though he got more than 70 per cent in his final exam and won a prize for his industrial relations work.
He discovered, however, that the arrangements for mature students at Cambridge were different from those at Oxford. "Mature students are welcome in graduate colleges in a way that they are not in Oxford," he says. Then he discovered that St Edmund's would take students without A-levels. Before long, and after a very tough interview, he had embarked on a law degree.
But he had more setbacks. His back was still playing up. He had two more operations on it and had to drop out because of the pain. When he returned he switched to politics.
Although he has loved the academic work, it has been a struggle. Cambridge diagnosed him as dyslexic and he finds essay writing difficult under pressure.
But, like his son, he has found the ancient universities welcoming. "If there is anyone out there who has a speech impediment or dyslexia and takes heart from my experience, I am pleased."