British Prime Minister David Cameron was calling Tuesday on public sector unions to halt planned industrial action and accept that their pension packages are unsustainable and must be reformed. The Prime Minister was insisting the present arrangements are \"not fair to the taxpayer\" two days before a mass walkout of teachers, lecturers and civil servants, according to extracts released here from remarks he was making today. The Government is finalising contingency plans to deal with the biggest outbreak of industrial action since the coalition was formed, with up to 750, 000 workers set to stage a 24-hour walkout this Thursday. The stoppage, by members of four unions, will go ahead despite two hours of talks yesterday between ministers and union leaders to try to resolve a bitter row over pensions. With talks due to resume in July, Cameron was reported to have prepared a \"robust\" but fair message to unions in a speech to the Local Government Association annual conference today, officials said. The scale of the disruption will become clearer today as schools decide whether to close and parents learn if they have to make alternative arrangements for their children. The Trade Union Congress, an umbrella organisation, welcomed moves by the Government to meet again in July after ministers said they recognised that the funding basis for the scheme covering local government workers was different. However Mark Serwotka, leader of the Public and Commercial Services union, described the talks as a \"farce\", accusing the Government of having no interest in negotiating on plans to cut pensions, extend the Secretary Michael Gove that parents could volunteer to cover for striking tearetirement age and increase contributions. Mary Bousted, leader of the Association of Teachers and Lecturers, said \"We are disappointed, but not particularly surprised that the Government has yet again refused to give us the information we need to carry out negotiations about teachers\' and lecturers\' pensions.\" Cabinet Office minister Francis Maude and Treasury minister Danny Alexander maintained that the talks were constructive and expressed disappointment that Thursday\'s strike was going ahead because talks were ongoing. \"We can assure the public that we have rigorous contingency plans in place to ensure that their essential services are maintained during the strike.\" The National Association of Head Teachers said it had \"grave concerns\" about a suggestion by Education chers. For his part, general secretary Russell Hobby said \"It is probably not unlawful but we would strongly advise our members not to accept voluntary help to cover for absent staff this Thursday.\" Picket lines will be mounted outside schools, colleges, universities, Parliament, courts and government buildings such as the Treasury on Thursday, with many workers going on strike for the first time.