The Duchess of Northumberland has won permission to build a £3m tree-top haven behind Alnwick Castle.

Dubbed TreeTopia, it is a wooden tree house complex as big as two Olympic-size swimming pools that will be built near her husband's ancestral home.

The development will be part of grander plans - The Alnwick Garden - to transform the once-derelict walled garden behind the castle.

The first stage of the garden project featuring 12 acres of cascading waterfalls, rushing rills and spouting fountains at a cost of £10m, was opened by the Prince of Wales earlier this month.

Alnwick District Council granted planning permission for the grandiose plan on Wednesday.

The Duchess, Jane Percy, said yesterday: "We are all incredibly excited about this project and delighted that planning permission has now been granted."

TreeTopia is part of the Duchess's master plan for part of the Duke's extensive land which she originally started as a ''pet project''.

The tree house will involve a complex of inter-linking wooden buildings featuring suspended catwalks, rope and cable bridges as well as zip slides which will be more than 60ft above ground level.

It will be built to the eastern edge of the Alnwick Garden in mature woodland.