A Sark deputy believes the island will achieve full democracy in time for elections being staged at the end of this year.
Chief Pleas had voted to change its make-up in two stages over four years, but the UK government has insisted all members are elected on an equal basis.
In a letter to the Chief Pleas the Lord Chancellor Jack Straw said that way Sark met democratic principles.
Deputy Paul Amorgie said Sark had to grasp change.
"I think Sark is left with no alternative but to do as he requested," said Mr Amorgie.
"No matter how independent and remote Sark might like to think it is perhaps this reinforces the fact we have to respond to the wishes of the Privy Council and indeed her Majesty the Queen."
Currently owners of the island's 40 tenements (divisions of land) have an automatic seat in the Chief Pleas, and islanders chose 12 people's deputies.
But Sark needs to make constitutional reforms to comply with European human rights laws.
After much debate and under pressure to change, the Chief Pleas agreed in August to a compromise solution.
Twelve tenants would have guaranteed seats with the remaining being elected deputies.
A referendum in 2012 would then decide whether to go to a fully elected House.
But the Lord Chancellor and Secretary of State for Justice Jack Straw has now written to the Seneschal of Sark saying that option is against modern democratic principles, and to meet its international obligations Sark would need to elect all 28 members.
He says he is supporting what the people of Sark said they wanted when a referendum showed a clear majority in favour of the fully democratic option.
In his letter he said: "We do not underestimate the difficulties which you have encountered and the pressures you continue to face and we are keen to do whatever we can to help Sark complete this work of reform."
Chief Pleas will meet next month to approve the amended law and send it off for Royal Assent.