Britain suspended all aid to the Ugandan government on Friday over concerns that funding has been siphoned off into officials' bank accounts.
International development minister Justine Greening said payments worth £11.1 million ($17.6 million dollars, 13.8 million euros) that were due before the end of the financial year had been halted.
"Unless the government of Uganda can show that UK taxpayers' money is going towards helping the poorest people lift themselves out of poverty, this aid will remain frozen," the international development ministry said.
"We will expect repayment and administrative and criminal sanctions."
London provides some 27 million pounds of aid through the government in Kampala every year.
Britain, Denmark, Ireland and Norway had already suspended aid to the office of Uganda's Prime Minister Amama Mbabazi following claims that staff funnelled 10 million euros ($12.7 million) from an aid programme into private accounts.
Uganda's auditor general reported last month that money intended to help develop areas devastated by the war against the Lord's Resistance Army rebels had been stolen.
A dozen Ugandan officials have been suspended pending investigations.
Ireland said this month that Uganda had pledged to repay four million euros to the Dublin government after apologising over the missing funding.
Some 16 million euros of Irish funding that were due to Kampala this year will remain suspended while the investigation continues.
The development ministry in London said it was not yet clear whether British aid had been misspent.