Assuming givendob is required, the following result was found.
'%' OR @GivenForenames = '') AND (Surname LIKE @GivenSurname OR @GivenSurname = '') AND (CONVERT(VARCHAR(10),DOB, 103) = @GivenDOB OR @GivenDOB = '') AND (@GivenRef'' OR @GivenForenames'' OR @GivenSurname'' OR @GivenDOB'') -- The TOP 100 is what...