Three Kenyans who allege they were tortured by the British colonial authorities during the 1950s Mau Mau uprising are to begin a damages case at the High Court in London later.
It is the latest stage of a legal battle by veterans of the rebellion to sue the UK government.
Hundreds of elderly Kenyans claim they were the victims of brutality at the hands of British colonial officials.
The government has previously said it was not liable.
Papers in the test case were first served on the UK in 2009.
Last year a High Court judge ruled the claimants – Paulo Muoka Nzili, Wambuga Wa Nyingi and Jane Muthoni Mara – did have an arguable case.
BBC World Affairs correspondent Peter Biles says the three Kenyans, who are now in their 70s and 80s, will be giving evidence in pursuit of damages.
This week’s hearing will have access to an archive of 8,000 secret files that were sent back to Britain after Kenya gained its independence in 1963.
The Foreign Office says the Mau Mau issue remains deeply divisive, and this period of Kenyan history caused a great deal of pain for many on all sides.
It has indicated it would defend the claim “given the length of time elapsed and the complex legal and constitutional questions the case raises”.
According to the claimants’ solicitors, Leigh Day and Co, ministers will be now arguing that the claims are time barred and should be thrown out by the High Court.
The claimants are being supported by the Kenyan government and three academic experts on the so-called Kenya Emergency, which lasted from 1952-60, have made lengthy statements in support of their allegations.
A fourth claimant, Ndiku Mutwiwa Mutua, has died since the High Court ruling in July last year that the test case could go ahead.