It is the latest announcement ahead of a speech on Monday by Reform’s shadow chancellor Robert Jenrick to formally unveil the party’s welfare plans.
“Forcing British workers to pay for the benefits of foreigners is not just economically illiterate but plain immoral,” Jenrick said in a statement.
“People are more than happy to support their neighbours in hard times, but the British taxpayer cannot afford to subsidise everyone on the planet, especially those who have not paid in.”
This year the government expects, external to spend a total of £322bn on welfare in Great Britain, or 10.6% of GDP, just over half of which goes to pensioners.
Reform says it has spent six months drawing up a 50-page plan that it claims will save a total of £50bn a year.
On Saturday, the party said it would replace the disability payments system, Pip, if it entered Number 10 at the next election.
The latest proposals would ban foreign nationals from almost all welfare payments including housing benefit, pension credit, jobseeker’s allowance, child benefit, free childcare and disability benefits.
Only a small number of exemptions would apply, including the war widows pension and Armed Forces compensation.
The party had previously pledged to ban foreign nationals from claiming Universal Credit.