Anthony Delima-Bey, aged 32, of West End Road, Ruislip, also pleaded guilty to conspiracy to supply cocaine. He was sentenced to 22 years in prison.
Both men were coming towards the end of their sentences at HMP Springhill and being let out on day release, the aim being to allow them the opportunity to find work and reintegrate back into the community.
They exploited these opportunities to re-establish ties with their criminal associates and continue their drugs enterprise.
The supply network needed a structure and support from others outside of prison. This was facilitated by seven others, who conspired to transport and supply drugs from London/Hertfordshire to Northamptonshire.
During the course of the investigation, officers found 500g of cocaine with 78 per cent purity and tens of thousands of pounds in cash.
Pieces of paper containing a tick list with names and numbers, believed to be a dealers list, were also uncovered.
There were high value amounts on the list with the largest value being £969,000.Police drugs expert testimony revealed that the tick list referred to debts amounting to £13 million.