The primary facts are not in dispute. The consent and approval was given on 25 March 1976, and would become void "if the building work to which it refers is not substantially commenced within twelve months after the date of the approval" (s. 315). Although the section empowers the council to extend the approval beyond the time referred to, no extension was granted in the present case. The critical date, therefore, is 25 March 1977. No work of any relevance was undertaken on the site until a few days prior to that date. Preliminary engineering drawings covering the whole work had been prepared by Macfield's engineering consultants, and lodged with the council on 18 February 1977 for approval, but they were not in sufficient detail to serve as a basis for calling tenders for its construction, and no tenders were invited. Then on 21 March 1977 the consultants prepared a final plan covering only a reinforced concrete slab which represented part of the ground floor of one of the proposed units. This drawing was approved by the council on 22 March 1977. At that time a builder, Phillips Constructions Pty. Ltd. ("Phillips") was engaged on another building project for Macfield, and arrangements were made verbally for that company to lay the slab immediately upon receipt of the approved plan. The work required a small amount of excavation and levelling of the natural ground surface, the preparation of formwork, the placing of the steel reinforcement, and the pouring of the concrete. The steel was laid on 25 March, and the concrete poured on the same date. An officer of the council was present during the pour, and the Chief Building Inspector's report shows that approximately eight cubic metres of concrete was laid. The area of the slab is 7.125 metres square with a rectangular "bite" out of one corner measuring 3.3 metres by 2.2 metres. Its area amounts to approximately eleven per cent of the concrete slab area of the ground floor of the project. Phillips charged Macfield $2,127.17 for the work, but claimed that this only represented actual cost, and that if all items including profit of $1,000 had been charged the figure would have been in excess of $3,600. The appellant has challenged this figure, and there is evidence that a proper charge would have been about $900, or with profit, $1,200. The cost of the whole project as at March 1977 is estimated to have been approximately $350,000.