The Duke of Wellington was entertained in its tearoom and dairy maids made butter in its creamery for decades - and now Kenwood Dairy will be restored to its former glory.

The buttery in the grounds of Kenwood House has been out of action since 1929 when it was commandeered for residential use. But now, thanks to a �3.9million grant from the Heritage Lottery Fund to restore the historic estate, the three derelict Grade II-listed buildings will be smartened up and ready for visitors in time for autumn 2013.

The refurbishment of the dairy - built by the second Lord Mansfield as part of a model farm for his wife – will also allow community groups such as Heath Hands and the RSPB to use some of the buildings.

Tony Ghilchik, of the Kenwood Dairy Restoration Trust which tried to help raise funds for the project before English Heritage stepped in, said it was high time that the late 18th Century dairy, with its Georgian tiles and marble sinks, and the octagonal tearoom was treated to a makeover.

“It seemed such a shame to let the buildings sit there out of action,” said Mr Ghilchik, the trust’s treasurer.

“The state of the buildings is obviously getting worse and worse each year. It’s not a collapsing hunk of brickwork, but the guttering is falling off and it needs to be refurbished while it is still reasonably healthy.”

The main house closed in April for planned repairs to the grand building’s roof and peeling paintwork.

The interiors of the breakfast room, Lord and Lady Mansfield’s dressing rooms and the housekeeper’s chamber – designed by celebrated architect Roberts Adams – will also be restored.

Tim Reeve, historic properties director at English Heritage, said: “This grant will allow us to restore Robert Adam’s wonderful rooms, re-create the atmosphere of an 18th Century home and through our work with volunteers and the local community, breathe new life into the house and the estate.”

To celebrate the announcement English Heritage is hosting a free garden party in the grounds on Saturday (June 16) between 11am and 4pm.

Guests will be treated to special guided tours of the house while it is empty of its furniture and a rare trip to the dairy where maids will be making butter.

For more information visit www.english-heritage.org.uk