JUDGMENT

VERMA, J.:— These appeals by special leave are by several industrial concerns against the Andhra Pradesh State Electricity Board (hereinafter called the Board) challenging the common judgment of the Andhra Pradesh High Court in writ petitions filed by these concerns challenging the revision of the electricity tariffs by the Board by its proceedings contained in B.P. Ms. No. 1014 (Commercial) dated 13-12-1983 which came into force on 15-1-1984. Prior to this revision, the tariffs were governed by B.P. Ms. No. 418 (Commercial) dated 12-1-1981. On 13-121983, two separate orders were issued by the Board revising the various tariffs. By one of them, namely, B. P. Ms. No. 1014, the tariffs for various categories of consumers including H.T. categories 1 and 11 were revised. By the other order of the same date, namely, Memo. No. DE/COML/IV/2250/83/I, the tariffs for high power intensive industries were also revised upwards. Out of the appellants, it was applicable to five units, namely, (1) Nav Bharat Ferro Alloys Ltd., (2) AndhraSugars Ltd., (3) Ferro Alloys Corporation Ltd., (4) Grindwell Norton Ltd., and (5) A. P. Carbides Ltd. This upwards revision of tariffs made by the Board by its two orders dated 13-12-1983 which were made effective from 15-1-1984, was challenged by the appellants in writ petitions filed in the Andhra Pradesh High Court on various grounds. The High Court rejected all the grounds and dismissed the writ petitions by its common judgment now reported in AIR 1985 Andh Pra 299. These appeals by special leave are against the High Court judgment.

2. The appellants are all H.T. power consumers of one category or other. The tariffs consist of three parts : Part-A, Part-B and Part-C. Part-A provides for H.T. tariffs; Part-B for L.T. supply; and Part-C provides, inter alia, for miscellaneous and general charges. H.T. consumers in -P;rt-A are broadly classified into three categories: H.T. Category-1 (Industrial); H. T. Category-11 (Non-Industrial,); and H. T. Category-111 comprising of power intensive consumers and some others. The Board retained the power to decide in accordance with the guidelines as to which industries were power intensive and which were not. This was the position in the tariffs of 1975. Subsequently, the Board began to deal with the power intensive industries by notifying tariffs for them separately from time to time. In effect, there were four classes of consumers availing H.T. supply: (1) H. T. consumers falling under H.T. Category-1 (Industrial); (2) H. T. consumers falling under H. T. Category-II (NonIndustrial); (3) H. T. consumers falling under the category power intensive industries; and (4) H. T. consumers availing supply of electricity for irrigation and agricultural purposes included in Part-B. The tariffs for these different categories of H.T. consumers 1 were enhanced from time to time. For H. T. Category-1 (Industrial), it was 21 paise in 1975, increased to 30 paise in 1979, 33 paise in 1980, 40 paise in 1981 and 48 paise in 1984. Likewise, there was corresponding increase in the energy rates for H.T. Category-II (NonIndustrial), being 28 paise, 37 paise, 40 paise, 47 paise and 56 paise. The tariffs for power intensive industries were, however, increased by separate notifications issued by the Board from time to time. It was 11 paise prior to 1975, raised to 12.2 paise in 1977, 16 paise in 1978, 18.5 paise in September 1979, 21 paise in November 1979, 25 paise in 1980, 32 paise in 1981 and 45 paise in 1984. The H. T. consumers grouped in Part-B were required to pay 15 paise under the 1975 tariffs and 16 paise thereafter. Besides the energy charges as stated above, the H.T. consumers were also required to pay at different rates effective from 1-9-1982 an -additional charge levied fuel cost adjustment charges. The H, T. consumers.were also required to pay some amount as voltage surchargein accordance with the terms of the agreement entered into by the individual consumers with the Bo