JUDGMENT

VENKATACHALIAH, C.J.I. - In these appeals and special leave petitions brought up by the Revenue the short but interesting question that arises is whether Rule 1-BB of the Wealth Tax Rules, 1957 is a provision which affects and alters the substantive rights or is merely procedural. The further sequential and cognate question is whether the Rule is attracted to all proceedings pending at its enactment. The said Rule 1-BB concerns the mode of valuation of house-property wholly or mainly used for residential purposes, for the purposes of ascertaining the net wealth under the Wealth Tax Act, 1957.

2. Section 3 of the Wealth Tax Act is the charging section. It seeks to bring to charge for every assessment year the net wealth on the corresponding valuation date of every individual, Hindu undivided family and company. The expression "net wealth" is defined in Section 2(m) of the Act. Section 2(q) defines the "valuation date". Section 4 enumerates the assets to be included in computing net wealth. Sections 5 and 6 exempt certain assets in India an outside from being included in computing the net wealth.

3. Section 7 - and this provision is of particular relevance here - speaks as to how the value of the assets has to be determined. Section 7(1), as it stood during the relevant period, i.e., prior to 1-4-1989 when it stood substituted by the Direct Tax Laws (Amendment) Act, 1989 with effect from 1-4-1989 provided :

"7. (1) Subject to any rules made in this behalf, the value of any asset, other than cash, for the purposes of this Act, shall be estimated to be the price which in the opinion of the Wealth Tax Officer it would fetch if sold in the open market on the valuation date."

4. The Central Board of Revenue in pursuance of the rule-making power conferred by Section 46 of the Act promulgated rules known as the Wealth Tax Rules, 1957. These were amended from time to time and Rule 1-BB - with which we are now concerned - came to be inserted by the Wealth Tax (Amendment) Rules, 1979 with effect from 1-4-1979. The relevant part of the Rule reads as under :

"1-BB. (1) For the purposes of sub-section (1) of Section 7, the value of a house which is wholly or mainly used for residential purposes shall be the aggregate of the following amounts, namely :

(a) the amount arrived at by multiplying the net maintainable rent in respect of the part of the house used for residential purposes by the fraction 100/8; and

(b) the amount arrived at by multiplying the net maintainable rent in respect of the remaining part of the house, if any, by the fraction 100/9 :

Provided that in relation to a house which is built on leasehold land, this sub-rule shall have effect as if for the fraction 100/8 in clause (a) or as the case may be, the fraction of 100/9 in clause (b), the fractions 100/9 and 100/10, respectively, had been substituted."

Sub-rule (2)(a) defines the expression "gross maintainable rent"; sub-rule (2)(b) defines "House" as including an independent residential unit and sub-rule (2)(c) the expression "net maintainable rent". Sub-rule (5), however, envisages a departure from the regime of sub-rule (1) and provides that where the Wealth Tax Officer, having regard to the facts and circumstances of the case, is of the opinion that it is not practicable to apply the provisions of the rules to such a case, he may apply the rule with the previous approval of the Inspecting Assistant Commissioner.

5. The principal question in these cases is whether this rule is a provision of substantive law, not expressly rendered applicable to the valuation for the earlier years, and, therefore, only prospective or whether it is merely procedural attracted to all pending cases.

6. We have herd Shri J. Ramamurti, learned senior counsel for the Revenue and Shri Raja Ram Agrawal and Shri G. Sarangan, learned senior counsel for the assessees. In some of the cases in this batch, there are some delays in filing them. We condone the delays. We grant special leave in