The school in question is an "independent school". It is subject to registration requirements, and to inspection to ensure that it meets regulatory requirements. (See my previous post for the regulations.) Whatever inspection has been done has failed to turn up the materials in question, which were only disclosed when the teacher filed his employment complaint -- somewhat unsurprisingly, since they seem to have been in Arabic.
Enforcement activities in any area depend on violations coming to the attention of enforcement agencies. Complaints or reports are how most violations of laws and regulations come to official attention. It would be reasonable to think that this particular situation would be unlikely to come to official attention through complaints, since parents who send their children there are likely to know exactly what goes on and to approve of it. One might imagine that quite a lot of resources would have to be devoted to investigating if complaints aren't made about perceived violations such as this.
The materials have come to official attention now, and it might be safe to assume that an investigation will be conducted.
Ofsted, the inspecting body, had this to say in an annual report:
http://www.archive.official-documents.co.uk/document/ofsted/hc102/102-10.htm331 Other key concerns recorded in inspections carried out by OFSTED were:
... the breadth of the curriculum for pupils attending some religious schools, schools specialising in preparing pupils for the entrance examinations of selective independent schools, and some theatre schools;
...
332 The curriculum provided for pupils in some specialist schools, for example theatre schools, remains narrow and unbalanced. In some religious schools the curriculum is broad. In one evangelical Christian school, for example, despite a relatively short taught week, all areas of the curriculum are represented within what is a distinctive and coherent pattern of topics. In other religious schools, however, the balance is unsatisfactory. Many religious schools provide a pattern of religious instruction throughout the morning, with an inevitably limited secular curriculum delivered in two hours a day in the afternoons. Even where the balance between religious and secular studies is different to this, the amount of time available for the core subjects is sometimes inadequate and this can pose severe problems in GCSE courses, for example the lack of opportunity for investigation in science. The creative and aesthetic areas of the curriculum are often poorly represented or non-existent. Schemes of work are often not available.