You might find this fact sheet interesting.

The United Kingdom still has amounts outstanding from World War II and its immediate aftermath which it continues to repay on a regular basis. World War II-era claims on Iran have been incorporated into the claims being adjudicated by the Iran-U.S. Claims Tribunal, established after the 1979 Iranian revolution. Lend Lease claims against the former Soviet Union arising from World War II were settled in a 1972 agreement between the U.S. and U.S.S.R. In the 1972 agreement, the U.S.S.R. pledged to make three initial payments totaling $48 million and to repay the remaining Lend Lease debt once the United States had granted Most Favored Nations (MFN) trade status. The Soviet Union made the three initial downpayments, but because it did not obtain MFN status at that time – because of conditions set forth in the 1974 Trade Act – its obligation to make the remaining payments toward its Lend Lease debt was not triggered before the dissolution of the U.S.S.R. However, MFN status was extended to the Russian Federation in 1992, and accordingly, in 1993, Russia signed an agreement with the U.S. in which it acknowledged its liability and agreed to a repayment schedule for the former U.S.S.R.'s Lend Lease debt. Finally, the U.S. continues to work for a resolution with Taiwan of the issue of debts arising from World War II-era loans extended to China.

(Note, this document was written in 2000. UK paid off it’s WWII debts in 2006.)