By the end of the first world war, the most a police constable could earn was 48 shillings a week – less than an unskilled labourer in an engineering factory, and just one-third the sum a munitions factory worker could take home.

This was also a period in which industrial militancy was re-emerging. In 1918, fewer than 6 million days were lost to strikes throughout the UK; the following year the number rose to more than 35 million. The police were not immune to this trend.

The National Union of Police and Prison Officers had never been recognised by the government, but this did not stop it submitting a claim for better pay, war bonuses and improvements to the pension scheme over the summer of 1918.

When the authorities failed to respond, the union called its members out on strike. On the morning of 30 August 1918, most of the Metropolitan Police's 12,000 officers were out. The picture here shows Jack Hayes, secretary of the NUPPO addressing a rally on Tower Hill.

The government was taken completely by surprise. The home secretary had earlier assured his colleagues that there was no cause for alarm, and gone on holiday.

By some accounts, the first prime minister David Lloyd George knew of the strike was when a detachment of Guards replaced police officers at the front door of Number Ten.

With no real contingency plan beyond the need to deploy troops in place of striking police officers, Lloyd George entered into negotiations with the union and succeeded in buying it off.

At the same time, however, he was laying the groundwork for retaliation – and less than a year later, he was ready to act.

The Police Act of 1919 made it illegal for police officers to join a trade union, and illegal for them to go on strike. It also established a new "company union", the Police Federation, as a non-militant representative body for police officers.

Faced with a threat to its existence, the National Union of Police and Prison Officers again called a strike. This time, however, it had misread the mood of its members. Fewer than 1,200 of the Met's 18,200 officers responded.

In Liverpool, support was stronger. Some 954 of the 1,874 police officers in the city joined the strike – marching on police stations which had not come out in a bid to gather further support.

Although troops were once again deployed, civil order rapidly broke down. Robberies, burglaries and other crimes soared. Within days, huge crowds were gathering on Scotland Road to systematically loot shops and other commercial premises.

Even the presence of armed troops – and tanks – on the streets did little to deter disorder. When magistrates read the Riot Act, they came under a barrage of rocks that forced them to shelter inside an armoured car.

Eventually, it took a bayonet charge to disperse the hard core of rioters.

With little support elsewhere in the country, however, the strike was doomed. Within days, those who had gone out were dismissed. It took less than a week to recruit replacements from the ranks of demobbed soldiers.

In all, 955 Liverpool police officers were dismissed, along with more than 1,000 from the Metropolitan police. Smaller numbers from the City of London, Birmingham, Bootle and Birkenhead were also sacked. None was ever reinstated. All lost their pensions

Utterly broken by the outcome of the strike, the National Union of Police and Prison Officers rapidly went out of business. Its successor for the past 90 years has been the Police Federation.

Picture: bayonet fixed, a solder guards the remains of a looted Liverpool shop.