There is currently no agreement between the United Kingdom and Belarus.
However pending the entry into force of a United Kingdom/Belarus double taxation agreement, (the “Double Taxation Relief (Taxes on Income) (Belarus) Order 1995” No. 2706) both Belarus and the United Kingdom will continue to operate the agreement between the United Kingdom and the Soviet Union, in respect of their residents. See the entry for the Soviet Union for details of this agreement.
As at August 2008 the 1995 agreement is unlikely to enter into force in the near future.
The text of the Tax Treaty can be found via https://www.gov.uk/government/publications/belarus-tax-treaties