The disclosure comes after Canadian Kenneth Law, 57, was arrested in Ontario and charged with counselling and aiding suicide after allegedly selling a lethal substance to people across the world.
Mr Law is accused of sending 1,200 packages to 40 countries and is now also being investigated by police in the United States, Italy, Australia and New Zealand.
British police began investigating in April after receiving information that a number of people in the UK had purchased products on Canadian websites which sold substances to assist suicide.
In total, 232 individuals in the UK were identified as having purchased products from the websites in a two year period up to April 2023.
The NCA said that 88 of those people have died.
The law enforcement agency added that “at this early stage there are no confirmed links between the items purchased from the websites and cause of death in any of these cases".
National Crime Agency deputy director, Craig Turner, said: “Our deepest sympathies are with the loved ones of those who have died. They are being supported by specially trained officers from police forces.
“In consultation with the Crown Prosecution Service, the NCA has taken the decision to conduct an investigation into potential criminal offences committed in the UK. This operation is underway."
Canada’s Peel Regional began its own investigation in April following the sudden death of an adult in the Toronto area.
Since Mr Law’s arrest, police forces across the UK have been making checks on everyone who ordered the substance.
The former chef, who is in custody in Canada, is due to appear in court again later this month.
Under the Canadian criminal code, counselling or aiding a person to die by suicide can result in a 14-year prison sentence.