Royal Mail parent International Distributions Services (LSE:IDS) has rejected a bid by West Ham co-owner Daniel Křetínský.
However, Křetínský is said to be readying further offers.
Křetínský made a cash offer to buy the entirety of IDS, but this was rejected, his EP Group confirmed on Wednesday.
“As a committed long-term investor in the UK, EP Group recognises the importance of the Royal Mail business to its various stakeholders,” the firm said in a statement.
“[This includes] employees, trade unions, customers and government, as the UK’s sole designated universal service provider.
“EP Group has submitted its non-binding indicative proposal to IDS with the interests of these important stakeholders in mind.”
Křetínský already owns 27.5% of IDS, alongside holding around 27% of West Ham United, as well as a significant stake in J Sainsbury PLC.
Previously a lawyer, Křetínský has become an energy tycoon as owner of energy firm Energetický a Průmyslový (EP), which operates in several European countries, including the UK and Germany.
His attempts on Royal Mail come after the firm was privatised in 2013, but has struggled in recent years, including with efforts to meet its six-day letter delivery obligations.
EP Group also referenced these, claiming it would be “prepared to support this iconic business as it transforms and rebuilds into a modern postal operator”.
“Weak financial performance, poor service delivery and a slow transformation, in the face of a market going through structural change, have put the business under unsustainable pressure,” it said.
“With the increasing competition from multinational companies in the UK postal market, private investment in Royal Mail becomes crucial.”
Shares jumped 17.6% to 251.80p.