Samantha Cameron’s step-father has accused the Scottish Nationalists of launching a ‘Mugabe-style land grab’ against owners of country estates.

William Astor, the 4th Viscount Astor, said that estate owners would worry that ‘we will find ourselves regarded as foreigners again in our own country’.

Scottish First Minister and SNP leader Nicola Sturgeon wants to reform Scotland’s land laws and put one million acres of land into public ownership by 2020.

Fears: Lord Astor, pictured with wife Annabel warned estate owners would worry that ‘we will find ourselves regarded as foreigners again in our own country’

Landowners could be forced to sell if the Scottish government decides their ownership is a ‘barrier to local economic and social development’.

Shooting estates will also lose vital tax breaks. David Cameron has shot stag at the Astors’ 20,000-acre Tarbert estate on the Hebridean island of Jura.

In an article for The Spectator magazine, Lord Astor warned the policy could have the same effects as the Zimbabwean dictator Robert Mugabe’s attacks on white farmers. He wrote: ‘ Are we estate owners now to be nationalised or made to feel so unwelcome that we have to sell up in a Mugabe-style land grab?

‘It would be a pity, but we are accused of owning too much.’

The hereditary peer added: ‘ The worry is that it will not actually be for the benefit of the local community but will hand power straight to the bureaucracy in Edinburgh. Under the SNP, governance has already been centralised there. “Benefit to all” must mean all, not just special interest groups. ’

20,000 acres: The Astors' Tarbert estate on the Herbrides island of Jura in Scotland where David Cameron has shot stag

He questioned if the SNP attack on estate owners was because ‘we don’t sound Scottish’.

‘We should not all have to sound like Rob Roy,’ Lord Astor said. ‘If the SNP wants us all to speak with a certain type of Scottish accent, what does that say to the many hundreds of thousands in the immigrant community who have lived in Scotland for a long time but still speak with the accent of their birth? Are they not Scottish? ’

Lord Astor went on: ‘ West coast Scottish estates require constant investment, but the beauty and ambience of the place, the people and its culture have always made it all worthwhile.

Scottish First Minister and SNP leader Nicola Sturgeon wants to reform Scotland’s land laws and put one million acres of land into public ownership by 2020

‘Following the SNP victory, however, families like us worry that we will find ourselves regarded as foreigners again in our own country. The SNP manifesto promises ‘‘to ensure Scotland’s land reform debate focuses on how Scotland’s land can be best managed in the public interest to ensure it is of benefit to all of the people of Scotland’’.

‘Scotland is different from England and, contrary to many views including those of the SNP, its rural policies already work well.

‘The SNP won nearly all the Westminster seats in Scotland with 50 per cent of the vote – a remarkable feat for which they should be congratulated. But let them not forget the other 50 per cent who did not vote for them, whose voice still matters. ’

Last night a spokesman for Aileen McLeod, SNP environment minister in the Scottish parliament, said: ‘People in Scotland are having a mature and respectful debate on how land ownership can deliver greater public benefits, and Viscount Astor should consider whether some of his remarks meet the standards of debate that they expect.

‘The recent consultation on land reform shows that there is popular support for our proposals for an accountable and transparent system of land rights that promotes fairness and social justice, environmental sustainability and economic prosperity.

‘Respondents have provided a wide range of helpful comment on their reasoning for support or opposition.’ Lord Astor married Samantha Cameron’s mother Annabel in 1976 after her divorce from Sir Reginald Sheffield, making him the Prime Minister’s stepfather-in-law.