I thanked him, but explained that I had not yet completed my sentence for the murder of eleven men. Still he didn't give in.

I finally agreed to take the job of night watchman at the docks, with three pounds a week pay and accommodation provided: an abandoned Pullman railway carriage now became my prison cell. I suppose I might have continued my life sentence until the day I died, had I not come into contact with Master Harry Clifton.

Harry would claim, years later, that I had shaped his whole life. In truth, it was he who saved mine.

The first time I came across young Harry, he couldn't have been more than four or five. 'Come on in, lad,' I called to him when I spotted him crawling towards the carriage on his hands and knees. But he immediately leapt up and ran away.

The following Saturday he got as far as looking in through the window. I tried again. 'Why don't you come in, my boy? I'm not going to bite you,' I said, trying to reassure him. This time he took up my offer and opened the door, but after exchanging a few words, he ran away again. Was I that frightening a figure?

The next Saturday, he not only opened the door, but stood, feet apart, in the doorway, staring at me defiantly. We chatted for over an hour, about everything from Bristol City FC to why snakes shed their skins and who built Clifton Suspension Bridge, before he said, 'I'll have to be off now, Mr Tar, my mum's expecting me home for tea.' This time he walked away, but looked back several times.

After that, Harry came to visit me every Saturday until he went to Merrywood Elementary School, when he started turning up most mornings. It took me some time to convince the boy that he should stay at school and learn to read and write. Frankly I wouldn't have managed even that without the help of Miss Monday, Mr Holcombe and Harry's spirited mother. It took a formidable team to get Harry Clifton to realize his potential, and I knew we had succeeded when once again he could only find the time to visit me on Saturday mornings because he was preparing to enter for a choral scholarship to St Bede's.

Once Harry had started at his new school, I didn't expect to see him again until the Christmas holidays. But to my surprise, I found him standing outside my door just before eleven o'clock on the first Friday night of term.

He told me he'd left St Bede's because a prefect was bullying him - damned if I can recall the cad's name - and he was going to run away to sea. If he had, I suspect the boy would have ended up an admiral. But happily he listened to my advice and was back at school in time for breakfast the following morning.

Because he always used to come to the docks with Stan Tancock, it was some time before I realized Harry was Arthur Clifton's boy. He once asked me if I'd known his father, and I told him yes, and that he was a good and decent man with a fine war record. He then asked me if I knew how he died. I said I didn't. The only time I ever lied to the boy. It was not for me to ignore the wishes of his mother.

I was standing on the dockside when the shift changed. No one ever gave me a second glance, almost as if I wasn't there, and I knew that some of them thought I wasn't all there. I did nothing to dispel this, as it allowed me to serve my sentence in anonymity.

Arthur Clifton had been a good ganger, one of the best, and he took his job seriously, unlike his best mate, Stan Tancock, whose first port of call on the way home was always the Pig and Whistle. That was on the nights he managed to get home.

I watched Clifton as he disappeared inside the hull of the Maple Leaf to make some final checks before the welders moved in to seal the double bottom. It was the raucous sound of the shift horn that must have distracted everyone; one shift coming off, another coming on, and the welders needed to get started promptly if they were going to finish the job by the end of their shift and earn their bonus. No one gave a second thought to whether Clifton had climbed back out of the double bottom, myself included.

We all assumed that he must have heard the blast on the horn and was among the hundreds of dockers trooping through the gates, making their way home. Unlike his brother-in-law, Clifton rarely stopped for a pint at the Pig and Whistle, preferring to go straight to Still House Lane and be with his wife and child. In those days, I didn't know his wife or child, and perhaps I never would have if Arthur Clifton had returned home that night.

The second shift was working flat out when I heard Tancock shouting at the top of his voice. I saw him pointing to the ship's hull. But Haskins, the chief ganger, simply brushed him aside as if he were a tiresome wasp.

Once Tancock realized he was getting nowhere with Haskins, he charged down the gangway and began to run along the quayside in the direction of Barrington House. When Haskins realized where Tancock was headed, he chased after him and had nearly caught up with him by the time he barged through the swing doors into the shipping line's headquarters.

To my surprise, a few minutes later Tancock came running back out of the building, and I was even more surprised when Haskins and the managing director followed close behind. I couldn't imagine what would have convinced Mr Hugo to leave his office after such a brief conversation with Stan Tancock.

I found out the reason soon enough, because the moment Mr Hugo arrived on the dock, he gave orders for the entire shift to lay down their tools, stop working and remain silent, as if it were Remembrance Sunday. And indeed, a minute later, Haskins ordered them all back to work.

That was when it first occurred to me that Arthur Clifton might still be inside the double bottom. But surely no man could be so callous as to walk away if he'd thought, even for a moment, that someone might be trapped alive in a steel grave of their own making.

When the welders went back to work, Mr Hugo spoke to Tancock again before Tancock trooped off through the dockyard gates and out of sight. I looked back to see if Haskins was pursuing him again, but he was clearly more interested in pushing his men to their limits to recover lost time, like a galley master driving his slaves. A moment later, Mr Hugo walked down the gangway, climbed back into his car and drove off to Barrington House.

The next time I looked out of my carriage window I saw Tancock running back through the gates and once again charging towards Barrington House. This time he didn't reappear for at least half an hour, and when he did, he was no longer red-cheeked and pulsating with rage, but appeared far calmer. I decided he must have found Clifton and was simply letting Mr Hugo know.

I looked up at Mr Hugo's office and saw him standing by the window watching Tancock as he left the yard. He didn't move away from the window until he was out of sight. A few minutes later Mr Hugo came out of the building, walked across to his car and drove away.

I wouldn't have given the matter another thought if Arthur Clifton had clocked in for the morning shift, but he didn't, nor did he ever again.

The following morning, a Detective Inspector Blakemore paid me a visit in my carriage. You can often judge the character of a person by the way he treats his fellow men. Blakemore was one of those rare people who could see beyond his nose.

'You say that you saw Stanley Tancock leaving Barrington House between seven and seven thirty yesterday evening?'

'Yes, I did,' I told him.

'Did he appear to be in a hurry, or anxious, or attempting to slip away unnoticed?'

'On the contrary,' I said. 'I remember thinking at the time he looked remarkably carefree given the circumstances.'

'Given the circumstances?' repeated Blakemore.