World-famous designer Jasper Conran is trying to scupper a West farmer's plan to extend a "slurry lagoon" near his £8.5 million country mansion.

The fashion giant is worried Alan Tizzard's slurry pit is spoiling the character of Ven House in Milborne Port, near Sherborne, on the Dorset- Somerset border.

It is one of a number of planning applications said to have upset Conran, who bought the early 18th-century, Grade I-listed property two years ago.

Other proposals include a nearby nursery's plan to erect a series of green polytunnels and Mr Tizzard's racehorse trainer brother Colin's proposal to use more of his land for equestrian purposes and build a pub.

Conran, 49, who is worth at least £25m, believes the planning applications close to Ven House "threaten the undisturbed nature of its ancient character". Dairy farmer Alan Tizzard has submitted a retrospective planning application to South Somerset District Council for the enlargement of an existing slurry lagoon at Canon Court Farm, with associated tree planting.

In his objection, Conran said: "The house and gardens are undeniably beautiful, but the qualities of Ven come from much more than its architecture. To see new development in such proximity would damage, for ever, its exceptional qualities."

Conran believes such developments across the country are "nibbling away at part of our heritage". He said: "Nobody is going to build a slurry pit in front of Blenheim Palace or Woburn Abbey, but councils are letting it happen elsewhere. It is time for this reckless damage to stop."

His stance is being supported by English Heritage, which described the potential developments as "highly undesirable", and the Garden Society.

But Paul Huntington, senior environmental protection officer, said: "With this type of uncovered slurry lagoon, allowing a crust to develop will reduce odour and ammonia emissions from the store, particularly for cattle slurry."

Conran also objects to more trees being planted to hide the lagoon.

A letter to the council on his behalf said: "Although replanting along the lines of the original avenue might be beneficial, the suggested screening planting would itself add to the encroachment on the protected parkland – that is to say, the additional planting would be as intrusive as the damage it is designed to hide."

Mr Tizzard declined to comment on Conran's objection.

The first occupant of Ven House was lawyer James Medlycott, who built the house in 1725. It came with the added bonus of a seat in Parliament representing Milborne Port. However, within six years the cost of the property had contributed to making Medlycott bankrupt.