Daniel Kretinsky, nicknamed the “Czech Sphinx” for his inscrutable approach to investment, will be free to increase his stake in Royal Mail to more than 25% after Grant Shapps, the new Business Secretary, decided it would not raise security concerns. The announcement – ​​which clears the way for Mr Kretinsky to buy enough shares for a takeover bid – was followed by explosive exchanges between the company and union leaders, who are now threatening a rolling wave of strikes to destroy deliveries in Christmas. Mr Kretinsky is believed to support existing plans by Royal Mail executives to end Saturday letter deliveries after a dramatic drop in the number of mails sent. The change will require an Act of Parliament because Royal Mail’s obligations are enshrined in law. Unions are lobbying the company’s board to force a modernization program and have already called repeated strikes. In the hours following Mr Shapps’ decision, Royal Mail offered a new pay deal in the hope of breaking the deadlock. Bosses have offered a 9% pay rise over the next two years, including a 7% pay rise and a 2% lump sum payment. The offer comes with restrictions, however, with union leaders saying they must agree to a “turnaround program” that includes seven-day-a-week parcel deliveries, as well as cuts to sick leave and longer shifts during the busy winter season. . The Communication Workers Union (CWU) hit back with fury, accusing Royal Mail of “declaring war on postmen”. Union bosses at the CWU are due to meet on Tuesday to decide how to respond to the announcement, with a source saying further industrial action is likely. They said: ‘You could now see strikes until Christmas. “Our members are ready for it.” Kwasi Kwarteng, the former business secretary, launched an investigation into Mr Kretinsky’s creation of stakes through his investment arm Vesa earlier this year under the National Security and Investments Act 2021. He currently owns 22% of Royal Mail and is the company’s largest shareholder. Mr Shapps’ decision comes just weeks after a similar review was rejected into media mogul Patrick Drachi’s interest in BT. A spokesman for Vesa said it welcomed Mr Shapps’ decision and “reiterates[d] our commitment to continuing our long-term investment presence in the UK, including our partnership with Royal Mail.” Vesa is the second largest investor in Sainsbury’s. Mr Kretinsky’s varied business interests also include a stake in Premier League football club West Ham United, as well as Le Monde newspaper. He initially made his fortune by illegally buying coal and natural gas power plants over the past 15 years. Asked what Mr Shapps’ decision meant for the Czech billionaire’s plans to increase his stake in Royal Mail, a source close to him said last night: “We certainly have an opportunity to increase our stake. On the other hand, there is no need.”