PLANS for part of Scotland's new Parliament complex have been altered after the discovery of a long-forgotten tower.

The stump of the tower has been found sticking up into the roof space of Queensberry House, the five-storey, 17th century mansion on the Canongate destined to become the parliament's administration block.

Now experts at Historic Scotland are drawing up plans to recreate the original tower top, thought to have been destroyed 200 years ago.

The open-topped structure, measuring 20ft long by 10ft wide and with 2ft thick walls, will dominate the new parliament complex and become a new city landmark. It was in this mansion that the second Duke of Queensberry lived and drafted the 1707 Act of Union between Scotland and England.

The tower was originally used as a viewing platform called a belvedere, from which to look out on the neighbouring Palace of Holyroodhouse.

Discovery of the huge stump looming out of the darkness in the attic space took archaeologists by surprise during an intensive study of the whole site before construction starts next spring. They researched archive records and drawings and concluded that it was the original tower built about 1680 which was hacked down when the mansion was raised by a storey and re-roofed to form barracks about 200 years ago.

In a restoration project which will have no effect on the timescale for building the overall complex, the mansion and crowning glory will be returned to their original shape.

John Lowrey, a prominent Edinburgh University architectural historian, said: ''In its heyday this was a very lavishly appointed house with fantastically elaborate gardens. The point of building the tower in the first place would have been a symbolic kind of thing. It was saying 'I am the most important person around and don't forget it'.''