Veterans of Cold War experiments at the Porton Down research centre said the Government had "finally and belatedly" paid its dues after they were awarded £3 million compensation.
Ken Earl, founder of the Porton Down Veterans Support Group, said the settlement would allow members to get on with their lives, but criticised the amount of the award.
The money, which the Ministry of Defence said was "in full and final settlement" of their claims, ends a decade-long campaign for justice. It is understood the money will be shared equally among 360 veterans and their widows - which would amount to more than £8,300 each.
Announcing the award, which has been made without admission of liability by the MoD, defence minister Derek Twigg offered the Government's first full apology to the servicemen.
In a written statement to MPs, he said: "The Government accepts that there were aspects of the trials where there may have been shortcomings and where, in particular, the life or health of participants may have been put at risk. The Government sincerely apologises to those who may have been affected."
Mr Twigg said an "amicable" agreement was reached between the MoD and those who were subjected to chemical weapons testing at the site near Salisbury, in Wiltshire.
The ex-servicemen claim they were tricked into taking part in what they were led to believe were cold remedy tests at the centre in the 1950s and 1960s.
Mr Twigg said Britain's security had "rested" on the trials and the country owed participants a "debt".
Mr Earl, 74, welcomed the settlement, adding: "It will allow our members to have a degree of closure on this issue and get on with their lives. But from the money point of view it should have been a lot more. It's not even half the price of a tank by today's standards."
Mr Earl, who underwent tests at Porton Down in 1953 while in the RAF, added: "I haven't been well all my life and believe they damaged my nervous and immune system. What they put on my skin was the most deadly compound ever manufactured by man - sarin nerve gas - which is now described as a weapon of mass destruction."
