Two men were found living in a former toy shop surrounded by 775 cannabis plants, a court heard.
The electricity had been bypassed and British Gas said the power used for a 91-day period would have cost £46,477.
A black air pistol was also found at the property.
Robertas Cela, 36 and Fjoraldo Hazizi, 27, were arrested by police on 19 October after they carried out a warrant at the former Toys and Prams shop in Hill Street, Wisbech.
They found the 755 cannabis plants in the three-storey building, with the potential to produce a combined yield of between £211,400 and £634,200.
Cela and Hazizi were found on the first floor, with one living in a converted room with a bathroom and one sleeping in the corridor.
In interview, Cela told officers he was offered work to water the cannabis plants for £300 a month, while Hazizi said he was offered up to £8,000.
Both men admitted producing cannabis and were each sentenced to two years and eight months in prison at Cambridge Crown Court on Friday (16 December).
PC Matt Smart, who investigated, said: “This successful warrant allowed us to seize a large amount of cannabis and stop it from being sold on the streets.
“We rely on people in our communities being our eyes and ears because we can’t be everywhere. If something doesn’t seem quite right it more than likely isn’t, so please report it to us.
“We would urge people to look out for signs of illegal cannabis factories, including blacked-out windows, people coming and going at various times of the day and a distinctive ‘humming’ noise from fans and ventilation.”
Police say people can use this link they suspect drug activity in their area, report it to us on our website.
