Section 783BK | Election for partial relief
From legislation.gov.uk
(1)An individual may elect for partial relief to be given for a tax year if the individual's relevant property income for the tax year exceeds the individual's property allowance for the tax year (see section 783BH).
(2)An election must be made on or before the first anniversary of the normal self-assessment filing date for the tax year for which the election is made.