Highpoint Prison in Suffolk is at the centre of allegations involving sex, drugs and one of the UK's leading anti-drugs charities.
The two were ordered out of Highpoint Prison
Two women drug therapy workers have resigned from the charity after the Prison Service ordered them out of the jail.
The two women were confronted with allegations that they had had inappropriate relationships with two male prisoners.
Their employer, the charity Addaction, which has lost its contract at Highpoint, said the pair chose to resign.
The Prison Service then carried out an urgent review of security inside the jail.
There was concern about the level of drug abuse among prisoners.
At its peak more than a quarter of all drugs tests on prisoners were coming back positive.
Governor Roger Haley said drug taking at the prison had been reduced.
"We removed certain people from the prison who we don't think were helping us in our fight against drugs.
We're getting them before the prisoners do
"That certainly had the big effect. We've improved our searching of visitors and searching of the prison areas and that's bringing more drugs to light.
"We're getting them before the prisoners do."
In a statement, the Prison Service confirmed the two former drug workers were excluded from HMP Highpoint pending an investigation into certain allegations.
Addaction told BBC Look East: "It was another one of our workers who tipped off both the Prison Service and Addaction.
"Subsequently we were informed by the prison that it had suspicions over alleged drug trafficking.
" We do, however, take full responsibility for the behaviour of our staff.
"In this case two of our workers acted totally unprofessionally and in a manner which we deplore.
"Addaction dealt swiftly with this situation. We have since developed an action plan to minimise the chances of this kind of thing happening again."
Suffolk Police said they were investigating allegations of possible drug-related offences by contract staff working at Highpoint.