Red squirrels could soon be scampering through their native woodlands in Cornwall – but only after the grey intruders who forced them out are eradicated.

The Prince of Wales will launch a reintroduction project for specially selected parts of the county as he visits the Royal Cornwall Show today.

Landowners on the Lizard Peninsula and in West Penwith have already started culling greys, which are officially classed as vermin and must be wiped out in the area before any reds can be brought in.

The Prince, an ardent supporter of the case to preserve the species, said the importance of such schemes "cannot be understated".

He said: "They are one of the most charming and irresistible of British native mammals and are under ceaseless, pernicious attack by the relentless march of the imported greys, which do such untold damage to newly planted native hardwood trees all over the country."

Prince Charles is patron of the Red Squirrel Survival Trust (RSST), which is working with The Cornwall Red Squirrel Project to enlist landowners and farmers. Four supporters have already started culling greys on their land, but it will take at least three years before the habitat is safe for reds.

The scheme, which will cost £120,000 over three years, could prove a major tourism draw, and would include an environmental impact. Greys are far more destructive than the more timid reds, and have been blamed for fatally ring-barking hardwood trees such as oak. They are a threat to some birds and are considered a menace by many farmers because of the destruction they cause to crops.

The two areas of Cornwall were selected because they are surrounded by sea on three sides and can be protected from re-invasion by greys.

The red squirrel was last seen in Cornwall in 1984. Its disappearance is largely due to the competitive presence of the invasive greys, which carry a virus which is harmless to them but potentially deadly to reds.

Joshua Perry, director of RSST, said the success of the chough, which has recently been reintroduced in Cornwall, highlighted the possibilities. Despite the benefits, any cull is expected to be controversial.

But Mr Perry expects the backlash in Cornwall to be minimal. He said: "In rural regions people realise greys are total pests. They are vermin, and if you catch one, you have to dispatch it."

Charles Williams, chairman of the Cornwall Red Squirrel Project, which is locally managed and employs a full-time ranger, said the most humane method used to cull greys was poison.

The substance, which does not harm other wildlife, is placed in an L-shaped trap, so only squirrels, and rats and mice, can access it. Mr Williams said: "It's obviously a concern to people, but this method is approved by the Forestry Commission."