( 1 ) THIS is a writ petition whereby the petitioners seek quashing of the letters of demand issued by the DDA to the petitioners in respect of 5th and final instalments for the flats allotted to them on the ground that the same have been determined arbitrarily.

( 2 ) THE first petitioner is a Society of flat owners, registered with the Registrar of Societies. Remaining petitioners totalling 125, are the members of the Society who were allotted flats by the third respondent, DDA under Self Financing (Housing Registration) Scheme. Fourth respondent, the Deputy Director (H-1) is the functionary of DDA. While the first respondent is the Union of India, the second respondent is the Administrator of the Union Territory of Delhi and is the ex-officio Chairman of the third respondent.

( 3 ) THE third respondent came out with self Financing House Registration Scheme. This Scheme was announced and advertised in the edition of Hindustan Times dated 28/08/1977. An announcement was also-made by the DDA in the form of a pamphlet titled "your Investment for Your House" (for short Announcement"), The Announcement indicated that fla were to be constructed in Basant Enclave, Munirka, Hauz Khas and Sidharth Enclave. The prospective allottees were required to apply for the registration with the DDA from 15/09/197 7/11/1977. Subsequently, the DDA extended the closing date of the Scheme till 31/03/1978. As per the Announcement applications for allotment of flats to persons registered under the aforesaid scheme were required to be invited by the DDA in accordance with para 8 thereof. Para 8 of the Announcement reads as under:-

"applications from persons registered under this Scheme will be invited as soon as specific schemes have been prepared and construction is about to start. "

( 4 ) THE estimated cost of the flats were to be announced whenever specific schemes for construction of flats were to be prepared taking into consideration the location of the proposed flats, their specifications and design, cost of construction prevailing at the time of execution of the Scheme and fluctuation depending upon other relevant factors. As per para 6 of the Announcement, the following payments were required to be made by the applicants to the DDA:-

I) A sum of Rs. 10,000. 00 as deposit with the request for allotment of the flat; ii) 25% of the cost of the flat (inclusive of the amount paid as registration deposit) at the time of acceptance of the application for allotment of the flat under the concerned Scheme; iii) Half yearly payments after acceptance of the application for the scheme concerned to be paid as per below: - (a) 20% at the end of six months. (b) 25% at the end of one year. (c) 20% at the end of one and a half years. iv) 10% at the time of taking over possession.

( 5 ) ACCORDING to para 7 of the Announcement, the DDA was required to pay interest @ 7% per annum on the registration deposit upto the date of the acceptance of the application under the concerned Scheme. The DDA, however, was not liable to pay interest on the payments made by the applicant in respect of the cost of flat provided, the flat was made available to the allottee within two and a half years of the acceptance of the application for the Scheme under which he/her had applied. In case the flat was made over beyond a period of two and a half years, the DDA was liable to pay interest @ seven and a half per cent till the date flat was offered with possession to the allottee.

( 6 ) PURSUANT to the Announcement the petitioners other than the first petitioner applied for registration. After their registration, applications were invited on formulation of a specific Scheme. The Scheme was contained in a Brochure which is at page 58 of the court record. The Brochure indicated the details of location of the flats, number of flats which were to be constructed category-wise, the building plans etc. The brochure also gave information with regard to the estimated cost of each categ