Subject to paragraph 2 below, the assessor for each valuation area shall, by such date before 1st April 1989 as may be prescribed, apportion the net annual value and the rateable value of those lands and heritages entered in the valuation roll which are part residential subjects as between the residential and non-residential use made of them.

The assessor shall, by such date before 1st April 1989 as may be prescribed, alter the valuation roll by adding to the entry of lands and heritages which are part residential subjects a note (an “apportionment note”) showing, separately from their net annual value and their rateable value, the parts of each of those values which relate respectively to the residential and non-residential use of the lands and heritages.