Frogmore Mill was also known as Frogmoor Mill and Covent Mill. It is first mentioned in the Ashridge Monastery Charter of 1253 operating as a felling mill, presumed to be a mill for fulling woollen cloth.  It had been converted to papermaking by 1774, when Edward Holmes leased the site. It was identified as Mill No. 401 in the excise list of 1816.  By 1803 the mill was acquired by brothers, Henry and Sealy Fourdrinier, of a family of important stationers in London, who installed the first mechanised papermaking machine in the world within the year. The machine was perfected by Bryan Donkin, from Nicolas-Louis Robert’s design – the first Fourdrinier type machine.  In 1804 a second improved machine was installed, followed by a third at Two Waters Mill in 1805. In 1810 the Fourdriniers became bankrupt.  In 1817 Frogmore Mill was purchased by The Grand Junction Canal Company and firstly leased to William Nash until his death in 1824, when it was taken over by his wife until about 1830.

Mechanisation brought increased consumption of raw materials and the supply of rags was insufficient. Much investigation went into alternative fibre sources.  Esparto grass from the desert regions was of particular significance. The link between Two Waters Mill and Frogmore Mill was re-established by G.W. Hayes when newsprint was made at both mills. In 1851 Hugh Burgess and Charles Watt made paper from wood by a chemical process, now known as soda pulp, for a newspaper trial.

Esparto grass was imported into the North of England as productive use of return trips, for ships exporting coal. Esparto was then transported by train to Boxmoor (now Hemel Hempstead Station) and therefore logically the mills used for its preparation were the two closest, Two Waters and Frogmore Mills. In turn these mills could supply Dickinson Company mills further downstream, (Apsley, Nash, Home Park, Croxley) when the company reorganised for the greater efficiency of each mill. Thereafter, each mill had a specific role within the production process, thus avoiding duplication.

John Dickinson and Company leased Frogmore Mill and Two Waters Mill to prepare esparto half stuff for their other mills, for a period of 10 years from 1877, after which trials of pulp production from a variety of vegetable fibres including bamboo, esparto and wood had been explored at Frogmore.

In 1890 Herbert Sanguinetti started the British Paper Company for recycling used paper. Initially, one machine produced paper and lightweight board for printers and laminators. In 1907 a second machine, (known today as Fourdrinier No.2) was installed under the direction of Cecil Sanguinetti, Herbert’s third son, who largely controlled the destiny of the Mill until his death in 1962 in his 90th year.

The British Paper Company continued until May 2000, when the Apsley Paper Trail charity took on the site to preserve its importance for future generations. The charity objective is to reveal and inform visitors and education groups, nationally and internationally, of the significance the Gade Valley paper mills played in the local community, in commercial papermaking internationally and the importance of paper as a very overlooked commodity.