-20the policy of accepting immigrants from the Mainland under the OWP scheme; (ii) Hong Kong’s ageing population; (iii) the rise in expenditure on CSSA. The Government regards the seven-year restriction as a rational response to the sustainability problem so arising: “Against the background of a serious fiscal deficit and the implication of demographic trends and characteristics identified in the [Task Force] Report, the Administration took the view that there was a strong case for applying a uniform 7-year residence requirement for providing heavily subsidized social services. In respect of CSSA, the Administration considered a 7-year residence requirement for new arrivals aged 18 or above to be a rational basis for allocation of social resources ...”48 54. Mr Cheung also puts forward certain other arguments championing the reasonableness of the rule, which I shall consider later.49 I wish first to focus on the question whether a rational connection exists between the avowed purpose of ensuring the financial sustainability of the social security system on the one hand and the seven-year residence requirement on the other. I propose to examine each of the three factors said to underlie the sustainability problem and consider whether they provide or contribute to a rational justification for the seven-year restriction. H. The OWP scheme H.1 The problem 55. The Task Force Report 50 explains the background and problem which had to be dealt with: “Under Article 24(2)(3) of the Basic Law as interpreted by the NPCSC Interpretation dated 26 June 1999, Mainland children born to Hong Kong permanent residents have the right of abode in Hong Kong provided that at least one of their parents have obtained permanent resident status by birth or residence at the time of birth of the children. In anticipation of the implementation of the Basic Law, the daily OWP quota was increased from 105 to 150 in 1995 to facilitate the entry of these children. 48 Mr Cheung’s Affirmation, §55. 49 In Sections K and L below. 50 At §§3.25 and 3.26.