The total deficit of U.K. defined benefit funds covered by the Pension Protection Fund's 7800 index increased 9.6% in December, to £86.4 billion ($117.3 billion).
The deficit was £78.8 billion at the end of November.
Deficits also worsened for the year ended Dec. 31, from £10.9 billion, said an update Tuesday by the London-based PPF. The PPF is the lifeboat fund for the defined benefit plans of insolvent U.K. companies.
The funding ratio of the corporate pension plans worsened slightly to 95.5% as of Dec. 31, down from 95.8% as of Nov. 30. The funding ratio was 99.4 % as of Dec. 31, 2019, the update said.
Assets were up 1.9% during the month and rose 7.9% for the year ended Dec. 31, to £1.83 trillion.
Liabilities increased 2.3% over the month and increased 12.3% for the year, to £1.92 trillion.
The FTSE All-Share index was up 3.9 % for the month and fell 9.8% for the year ended Dec. 31, the PPF said. Five- to 15-year index-linked gilt yields decreased 7 basis points in December and declined 59 basis points over the year.
As of Dec. 31, 60.3% of the 5,318 pension funds covered by the index were in deficit, compared with 60.5% as of Nov. 30. As of Dec. 31, 2019, 55.3% of the 5,422 pension funds were in deficit.
Commenting on the figures, Sion Cole, head of U.K. fiduciary business at BlackRock, said in an email that the slight fall in funding levels in December "was a result of liabilities increasing due to falling gilt yields, with 10-year yields ending the year at 0.25% and 30 year yields at 0.78%."
"While inflation expectations fell, investors remained nervous around the Brexit deal going down to the wire and the emergence of a new strain of the COVID-19 virus prompting tougher restrictions for large portions of the U.K.," he added.