More than 40,000 Kenyans are attempting to sue the British government for compensation in a second Mau Mau group action, alleging physical abuse or mistreatment during the insurgency against colonial rule in the 1950s.

The new litigation against the British Foreign and Commonwealth Office (FCO) has been lodged at the high court in London, and comes after the UK government last year paid out £19.9m to 5,228 Kenyans who suffered torture at the hands of the colonial administration during the uprising.

The payout marked the government’s first official acknowledgment of serious abuse committed during Britain’s messy withdrawal from Kenya. The foreign secretary, William Hague, told parliament that the settlement was “full and final”.

However, seven British law firms have been assembling new claimants, in some cases dispatching lawyers to Kenya and advertising for clients in local newspapers.

The new suit, according to the firms, involves 41,005 Kenyans and takes the form of a group litigation order, which allows related claims to be managed collectively. According to court documents filed in May, the high court will hear 25 test cases.

Unlike the first Mau Mau case, these new claims are not restricted to those who endured extreme physical violence. Claimants are seeking damages for a range of alleged offences, including false imprisonment, forced labour and an interference with their right to education.

Lawyers for the claimants say that a tentative trial date has been set for January 2016.

A spokesperson for the FCO said: “It is not appropriate for us to comment on a case that is going through the courts.” It is understood the FCO is due to file its defence by Friday.

The claims refer back to 1952, when the colonial governor, Sir Evelyn Baring, declared a state of emergency in Kenya in an attempt to quash a mounting anti-colonial insurgency known as Mau Mau. Over the ensuing eight years, an estimated 90,000 Kenyans were killed or injured.

More than 1 million were forced from their homes into detention facilities, which Kenya’s then attorney general Eric Griffith-Jones described as “distressingly reminiscent of conditions in Nazi Germany or communist Russia”. Some were Mau Mau rebels, but many were civilians caught in a dragnet of collective punishment.

Simon Myerson QC, who is instructed by Tandem Law on behalf of the claimants, says his clients suffered a variety of abuses, including castration. Each is seeking damages of between £1,000 and £150,000.

Lawyers also accuse the colonial administration of having crafted a system of torture or inhuman or degrading treatment. Under this formulation, Britain would be liable for abuse carried out by a variety of agents at the time —including the Kenya Police and Kenya Home Guard—on the grounds that the abusive “system” was imposed at the highest levels of office.

While the FCO has yet to file its defence, the Guardian has seen a copy of its informal provisional position statement, dated 6 September 2013. In it, the FCO denies responsibility for actions of the colonial administration. Referencing the first Mau Mau case, the FCO argues that the claims brought in this second suit “are conspicuously weaker”.

Lawyer Martyn Day, of Leigh Day, who orchestrated the 2013 settlement but is not involved in the second case, said: “It looks like the government has decided to batten down the hatches and fight them on the beaches and never surrender. Not surprising, when they’re facing so many cases.”

Leigh Day’s case involved members of Mau Mau veterans associations.

Lawyers for the claimants expect the FCO to plead limitation. In this event, they will ask the judge to use his discretion to exclude the time limit, using section 33 of the Limitations Act 1980.

In 2011, the FCO accepted that the Kenyans had been tortured, but it denied responsibility for the violence and later argued that the claims had expired.

In two rulings in 2011 and 2012, Mr Justice McCombe dismissed the FCO’s objections on liability and limitation, though these rulings are non-binding.

Tandem Law, a Manchester-based firm specialising in personal injury, began advertising for and registering new Kenyan claimants while the first case was under way. The firm represents 20,363 of the claimants, and is steering the case as lead solicitor.

In Kenya, there have been claims that litigation has had some adverse effects. Lawyers at the Law Society of Kenya said a number of elderly people had been targeted by imposter lawyers, some claiming to represent British firms, and defrauded of savings.

Kenyan media also report that the sudden influx of lawyers competing to sign up clients has caused confusion in some communities.

Bickering between Mau Mau groups has also become commonplace. Over the last two years, several associations have reportedly splintered, on the issue of how to proceed with legal claims.

George Morara, a former officer with the Kenya human rights commission who assisted on the Leigh Day case, says that the Commission had to set up an emergency hotline for settlement beneficiaries who find themselves targets for theft: “We said to the old men and women, ‘If you are threatened, call us.’ Some did and we intervened.”

The next public hearing on the case will be in December.

In 1960, Kenya’s state of emergency was ended and the Mau Mau detention camps were emptied. Back in London, officials kept mum on exactly what had transpired during Emergency rule. “If we are going to sin,” Kenyan attorney general Griffiths-Jones had written, in a 1957 memorandum, “we must sin quietly.”