TEN of Harrow's most historic amd interesting buildings are taking part in Open House, the annual celebration of London's architecture.

This weekend, the doors to many of London's most intriguing private buildings are opened freely and to everyone.

Harrow's rich architectural heritage will again feature strongly, with venues from Harrow School to White Magnolias, a new house built entirely of interlocking polystyrene blocks.

The borough recorded a 290 per cent increase the number of visitors to local Open House venues last year, and the organisers hope that this year the campaign will continue to raise the profile of places such as Headstone Manor, which is undergoing a major restoration.

Councillor Chris Mote, the leader of Harrow Council, said: "We are firmly committed to preserving all of our heritage venues and Headstone Manor is just one example of the many improvements that are currently taking place in Harrow.

"We are delighted to be a part of Open House and we very much hope that residents will make the most of the weekend to discover the hidden gems that are right here on their doorstep."

Venues across the borough that are included in Open House are: l The Grim's Dyke Hotel, Old Redding, Harrow Weald: the former home of W.S Gilbert, of "Gilbert and Sullivan" fame, who lived there from 1890 until his death in the lake in the grounds in 1911. The house was designed by Norman Shaw, one of the leading lights of the Arts and Crafts Movement.

l Headstone Manor, Pinner View, North Harrow: the former home of the Archbishops of Canterbury and Middlesex's oldest surviving timber-framed building. The 14th century grade-I listed manor house has undergone major restoration work by Harrow Council and will be open for free guided tours.

l Harrow School, Harrow-on-the-Hill: fans of the Harry Potter films will enjoy a visit to the Fourth form room, the scene of magic lessons in the Harry Potter and the Philosopher's Stone. The room dates back to 1615 and is Britain's oldest classroom. The Old Speech Room Gallery and the Museum of Harrow School Life will also open for visits during the weekend.

l White Magnolias, Bellfield Avenue, Harrow Weald: a house built entirely from interlocking polystyrene blocks and including such unusual design features as a double-height atrium, glass floors and even a glass staircase.

l East End Farm CottageMoss Lane, Pinner: a three-bay timber-framed yeoman house dating back to 1420. Original design features include an original part wall painting of a hunting scene on the dining room wall and a Tudor window upstairs.

l All Saints' Church, Uxbridge Road, Harrow Weald: Grade 11* listed, an excellent early example of the work of one of the best Victorian church builders, with stained glass by William Morris, Charles Kempe, and the Whitefriars. It features a monument to W.S Gilbert and sculpture by Josephine De Vasconellos. Organ recitals available.

l Pinner House, Church Lane, Pinner: The former rectory of the vicar of Harrow is a grade-11 listed, early Georgian house (1721) with pilastered front and magnificent oak-panelled dining room.

l Pinner Parish Church Hall, Church Lane, Pinner: This has a Royal Institute of British Architects award-winning glass and steel extension to the original hall. The adjacent 14th century grade-11* listed church is also open.

l St John the Evangelist's Church and ruin, Church Road, Stanmore: Victorian church ruin with bell tower providing views across London. The churchyard contains the tomb of W.S Gilbert. The churchyard also has ruins of a grade-11* listed 17th century church containing the tomb of the Victorian Prime Minister Lord Aberdeen.

At 2pm on Sunday, the Pinner Walk will include the historic High Street with its 15th and 16th century buildings and the parish church. The walk will take about 90 minutes and there will be a limit of people. meet outside Woolworth's in Bridge Street.

Open House programmes covering venues across the capital are available free from Harrow's libraries and the Civic Centre.

IN BRENT, Open House venues include the Town Hall; the Shri Swaminarayan Hindue temple in Brentfield Road, Neasden; Winston Churchill's bunker in Neasden; The Grange in Neasden; Old St Andrew's Church in Kingsbury; Alperton Cemetery chapel and crematorium; the Advait Cultural Centre in Wembley, and the Metron bingo club, formerly the State cinema, in Kilburn.

For further information, see www.londonopenhouse.org.