Chancellor Rachel Reeves has again refused to rule out a wealth tax - despite fresh warnings of "large-scale capital flight" from think tank Tax Policy Associates.
A report from the think tank says claims a wealth tax could generate £10billion are "implausible", The Times reports.
It adds that 80% of the potential revenue would come from just 5,000 people, and 15% from only 10 people, leaving the amount of money being generated from the tax vulnerable to change dramatically.
The report said: "A handful changing residence or valuations could remove billions."
However, Reeves appeared to hint at rejecting wealth tax proposals, saying the government's focus was on ramping up investment in the economy.
She said: “We’ve got the lowest private investment and the lowest total investment as a share of GDP of any country in the G7.
“The result of that is our productivity performance has not kept pace with our competitors and similar countries around the world.”