Wheelwrights are working to maintain the historic mills

Many of the mills are still being run commercially, while others are operated by volunteers.

The oldest post mill in England, at the rare dual Drinkstone Windmills in Suffolk, is among those being feted.

The Society for the Protection of Ancient Buildings (SPAB) has joined with the National Trust to host National Mills Weekend.

The society says that wind and watermills were thought to be in terminal decline in the 1950s, but since then, there has been a "renaissance" and the workhorse structures are now better cared-for and appreciated.

Still pumping

Several of the sites open to visitors are still hard at work, wind permitting.

Along with making flour and pumping water, mills have been used to produce paper and even gunpowder.

Sedge Fen at Wicken, Cambridgeshire, is the site of the only working wooden windpump remaining in the area. It was once used to drain and control water levels in the Fens.

Elsewhere in the county, Houghton Mill, a five-storey weatherboarded mill on an island in the Great Ouse, still turns out and sells flour.

In Essex, mills in Aythore Roding, Finchingfield, Mountessing and Stock are among those open for the weekend.