LUXEMBOURG, Dec 16 (Reuters) - U.S. life sciences company Illumina (ILMN.O) on Thursday criticised EU antitrust regulators for scrutinising its $8 billion cash-and-stock takeover of Grail (GRAL.O) even though the cancer detection test maker has no activities in Europe. The Commission"s decision to scrutinise the deal via a rarely used power marked a troubling change in its policy, Illumina"s lawyer told a hearing at Europe"s second-top court, the General Court. "If the Commission is going to radically change policy, then businesses should know. Think about business certainty," Daniel Beard said. Commission lawyer Nicholas Khan said Illumina"s arguments were incongruous, but Grail lawyer Javier Ruiz Calzado was equally critical. "The Commission has decided on a Copernican change in policy," he told judges, saying the policy change could hurt start-ups and the venture capitalist industry in Europe. EU antitrust chief Margrethe Vestager is seeking to extend her power to examine big companies" acquisitions of start-ups in order to shut down nascent rivals. Critics warn of over-reach while some national competition agencies worry about a power grab by the EU executive. The Commission, however, said it took up the Illumina case at the request of Belgium, France, Greece, Iceland, the Netherlands and Norway. Following a Commission order to seek its approval for the deal, Illumina complied but also launched litigation against the EU executive. Illumina riled the Commission when it completed the acquisition in August without waiting for the green light, resulting in an order to keep Grail separate and to have independent managers run the company until an EU decision. The deal, unveiled in September last year, would give Illumina access to Grail"s flagship Galleri blood test used to diagnose cancers at early stages when the disease is easier to treat. A judgment is likely to come next year. The case is T-227/21 Illumina v Commission.