Image: The large treehouse at The Alnwick Garden

A new report has found that The Alnwick Garden, an attraction established by the Duchess of Northumberland, has generated £150m in economic benefits since its opening in 2002.

The independent study was carried out by PricewaterhouseCoopers (PwC) and also showed that every £1 spent at the attraction generated £0.85 for the immediate local economy.

Around 3.8 million people have visited The Alnwick Garden - a figure which is four times initial expectations. More than half (59 per cent) are from outside the north east region.

The Alnwick Garden includes cannabis and opium growing inside the high security Poison Garden and one of the world's largest wheelchair-accessible treehouses.

The Duchess of Northumberland said: "When we said that we wanted to grow cannabis, opium and deadly nightshade, and secure wheelchair access to 50ft (15m)-high rope bridges, nobody believed it was possible.

"But we have stayed true to the vision and delivered an unparalleled, family-friendly, public attraction to rival anything in Europe. And the best bit is - there's more to come."

Details: www.alnwickgarden.com