Historian Hugh Sebag-Montefiore, whose Battle of the Somme book has just been published as a paperback, highlights a vivid record of the Somme written by a young private in the Suffolk Regiment.

Police Sergeant Sydney Fuller may have observed some terrible crime scenes on the beat after the Armistice ended the fighting on the Western Front. But he saw nothing to compare with what he witnessed on July 1 1916, when, as a 21 year old recruit in the 8th battalion, the Suffolk Regiment, he saw how the flower of British youth was cut down in a matter of hours during that hopeless, doomed first attack of the Battle of the Somme.

There were infamously 57,000 casualties during that first assault, and Fuller has become one of the prime sources used to tell subsequent generations how horrific it all was. His diary, which recorded the events he witnessed as they unfolded, is now a prized exhibit in London’s Imperial War Museum’s permanent First World War exhibition.

It did not take him long to realise that life on the Western Front was going to be no bed of roses. His diary entry for June 19 1916, the day when the 8th Suffolks marched to Bray, a town a short distance behind the front line, recorded his seeing ‘four dead horses beside the road. They had been blown almost to pieces by German shells.’

When eleven days later, the final preparations were being made for the great attack, Fuller’s commanding officer, according to the diary, told him and his comrades: ‘Kill all the Germans you can, and don’t take any prisoners’, adding that ‘the only good Germans were dead ones.’

The attack which commenced at 7.30am on July 1 1916, started promisingly as far as Fuller was concerned. Given he was in his brigade’s reserve battalion, he was only to go over the top if the Germans between the Somme villages of Mametz and Montauban repulsed the initial assault. As the French troops attacking on the right of the British went forward, Fuller saw ‘their bayonets glinting in the sunshine’.

The first British troops that retired from the fight were ‘walking cases, smiling and cheerful at the prospect of a time to be spent away from all this, possibly in Blighty [England]’.

Also the first German prisoners who followed in batches of around five to 25, did not appear very frightening. Fuller noted that ‘they were very dirty, looked half-starved and the majority were little’. They appeared to be ‘pleased to have got through alive so far’, and they ‘seemed to be afraid of us as if they expected to be shot at any moment.’

But when Fuller and his comrades were ordered to advance towards the British front line from the rear at around 10.45am, so that they could help capture a German redoubt, they were greeted with ‘a storm of enemy bullets’. Subsequently they were ‘heavily shelled’. Fuller was lucky to avoid injury when a shell splinter hit his ‘tin hat’. Others were less fortunate. ‘One man who got into the trench a few minutes after I did, was shot eight times through the buttocks by an enemy sniper. Had to step over one badly wounded man who was lying in the trench crying for help. We had to go on.’

But it was the gruesome sights in a nearby assembly trench which took his breath away: ‘Several of our men were lying in it, killed by the enemy’s shells. In one place, a man was kneeling, as if in prayer, his hands covering his face. Lying in the trench behind him was another man, face downwards, half buried in the earth thrown into the trench by the shells. A short distance away, another man was sitting on the fire step, buried to the knees, and looking as if he had suddenly turned to stone... And so on, here and there along the trench, wherever the enemy’s shells had dropped in.’

Fortunately for Fuller and his unit, the attack at the southern end of the British line, where his brigade was advancing, eventually cut through the opposition and took Pommiers Redoubt, the German stronghold that had been resisting. So he and his comrades were not called upon to go over the top. By mid-afternoon, the battle in Fuller’s sector had been lost and won. ‘The enemy’s guns were by now quite quiet, and only comparatively few of ours were firing,’ Fuller reported. They had survived.

However three months later, as he and his unit prepared to go into action again, this time against the Somme village of Thiepval, Fuller was given to understand that their lives would once again be in jeopardy: ‘The troops we relieved gave us the cheerful assurance that we should never take Thiepval, and also gave us terrible descriptions of the amount of artillery and machine guns the enemy had on this front. This, together with the knowledge that several divisions had tried to take the position, and failed, did not cheer us up very much.’

This time when the time came to advance at 12.35pm on September 26 1916, the British artillery was so intense Fuller described it as one great ‘thundering roar’. Although there was resistance in front of Fuller’s unit in the second German trench, it was soon overcome. ‘I saw a long line of men running towards our rear,’ he recalled, ‘and for a moment, I thought it was the beginning of another repulse. Then I saw they were holding their hands above their heads: they were Germans. They had surrendered, and left their trench like one man.’

As he moved around the battlefield, he spotted two dead German soldiers, who were lying near one of the dugout entrances. They had been riddled with bullets.

‘Another German, who was still alive, was lying buried almost to the neck by a shell which had dropped nearby,’ Fuller remembered. ‘I shall never forget the expression on this man’s face. It was ghastly white, and his eyes were staring with terror. He was unable to move, while our chaps threw bombs past him down the dugout stairs, and the enemy inside threw their bombs out.’

According to Fuller, the resulting explosions inside the dugouts could be ‘felt’ rather than heard. The sound was muffled by the depth of the dugout. While he was watching, ‘a little German popped out, wearing his metal helmet, holding both hands above his head, and crying “Mercy! Mercy!” He was shot at once, and dropped like an empty sack.’

While Fuller was walking northwards, looking for Zollern Trench, the second objective, he saw two more Germans running towards him. They were sobbing. One was wearing a Red Cross armband. Some British soldiers called out telling them to stop. But as Fuller said, ‘they seemed to be mad with fear, too terrified to be reasonable’. They dodged past the British soldiers’ bayonets, only to be shot by a passing party of bombers.

As for Fuller, not only had he survived another successful attack – Thiepval was duly taken – but this time his unit had surprisingly few casualties, approximately 40 men per company.

But another soldier later described what he saw when he stumbled across a mass of British dead left behind following the original attack on Thiepval which had taken place on July 1. He was ordered to search their bodies for identification disks. ‘It wasn’t a pleasant task,’ he noted, which in the circumstances was a classic piece of British understatement, a quality discernible in Fuller’s account as well.

The paperback edition of Hugh Sebag-Montefiore’s Somme: Into the Breach published by Penguin is out now price £9.99, as is the updated 75th Anniversary paperback edition of his Enigma: the Battle for the Code book with new material added, published by Orion’s Weidenfeld & Nicolson, £10.99.