Police discovered an £800,000 cannabis grow when they raided a large house next to a nursery in Derbyshire.

Derby Crown Court heard how 12 of the 19 rooms at the property had been adapted to grow the class B drug and the electricity had been by-passed.

Doors had been reinforced and all of the windows had been boarded-up from the inside.

Officers found Marsel Sadja and Saimir Kallau tending to the grow, having arrived in the UK from their home country illegally two months before.

Jailing both men for 20 months each, Judge Nirmal Shant QC said: “It is plain you would have had an awareness of the scale of this operation, 811 plants were found at the premises and there had been 253 previous plants already cropped.

“But the crown accept you had a limited function and had no influence on those in the chain above you. In colloquial terms you would be described as gardeners.

“Each of you had entered the country illegally and were paying off a debt.”

Sadja, 24 and Kallau, 23, both of no fixed address appeared over video-link from HMP Nottingham and were helped during the hour-long hearing by an Albanian interpreter.

Raglan Ashton, prosecuting, said police raided Heritage House, in Ironville, on December 16, acting on intelligence that cannabis was being grown there.

He said: “What they found inside was a fairly sophisticated and extensive cannabis grow. Each of the windows to the property was boarded up from the inside and the doors had been reinforced.

“There was CCTV covering the outside of the property and the electricity had been by-passed. There were industrial lighting units throughout the property and an extensive ventilation system had been installed.

“The property contained 19 rooms over four floors and 12 of them had been used to grow cannabis plants. There was a drying room and black bags in the property contained waste from a previous cannabis grow.”

Mr Ashton said in total 811 plants were removed from Heritage House and were analysed by a drugs expert.

He said if sold in wholesale quantities the estimated value was £80,500 to £319,600 and at a street level between £145,980 and £608,250.

Mr Ashton said there was evidence a further 253 plants had previously been grown at the property with a top value at street level of £189,750.

He said the top end valuation was therefore just short of £800,000.

Mr Ashton said: “These two defendants were found inside the property, both were taken back to the police station and refused to be interviewed.

“The crown say they must have had some awareness of the scale of the operation."

Both men pleaded guilty to being concerned to the supply of a class B drug.

Sonal Dashani, for Sadja, said: “He had come to the UK to find gainful employment and now faces custody.

“He would like the shortest sentence possible in order to get back to Albania as soon as possible.”

Alistair Grainger, for Kallau, said his client had been in the UK for two months and in Heritage House for just three weeks.

Mr Grainger said: “He is a man of previous good character and would like to express his remorse to the court through me.

“He had paid £15,000 to get to the UK and hoped to find gainful work as a painter and decorator.

“There were thinly-veiled threats and unpleasantries behind the scenes and he felt he had to do this to pay his debt off.”