The owner of the British postal service Royal Mail, International Distribution Services, said it has agreed to a £3.57 billion (€4.2 billion) takeover offer from Czech billionaire Daniel Kretinsky’s EP Group.

The offer would see EP Group buy IDS for 370p per share, while offering a series of “contractual commitments and intentions” to protect public service aspects of the Royal Mail.

IDS said if the deal goes through Royal Mail would continue its universal service obligation to one-price-goes-anywhere first-class post six days a week, and keep the company’s branding and UK headquarters.

It also said it would protect existing employment rights of all IDS staff, and that there is “no intention to make any material changes to overall headcount or reductions in the number of frontline workers” beyond existing plans.

IDS chair Keith Williams said both parties “are acutely aware of their responsibilities to IDS and particularly to the unique heritage of Royal Mail and its obligations as the designated universal service provider of postal services in the UK”.

“The IDS board has negotiated a far-reaching package of legally binding undertakings and commitments which provide our customers, employees and broader stakeholders with important safeguards.”

The potential sale has already attracted heavy scrutiny, with senior politicians and unions voicing concerns over the future of the postal service, which was privatised in 2013.

UK business secretary Kemi Badenoch met IDS bosses earlier this month for talks on the deal, and underlined the need to protect services for the vulnerable, those in remote areas and small businesses.

Shadow business secretary Jonathan Reynolds said on Wednesday: “Royal Mail is an iconic British institution with a unique place in our society and infrastructure. Labour will take the necessary steps to safeguard its undeniable identity and place in public life.

“These assurances are welcome that Royal Mail will retain its British identity and safeguard its workforce with no compulsory redundancies.”

Mr Kretinsky, who is already a 27 per cent shareholder in IDS, is said to be known as the “Czech Sphinx” and has a raft of other investments, including stakes in London football club West Ham United and supermarket giant Sainsbury’s.

He said Royal Mail is “part of the fabric of UK society and has been for hundreds of years”.

“The EP Group has the utmost respect for Royal Mail’s history and tradition, and I know that owning this business will come with enormous responsibility – not just to the employees but to the citizens who rely on its services every day.”

The bid comes at a crucial time for Royal Mail, which put forward plans to regulator Ofcom earlier this month to scrap second-class letter deliveries on Saturdays and cut the service to every other weekday as part of turnaround efforts.

Meanwhile, the UK’s communications watchdog Ofcom launched an investigation into Royal Mail last week, after it said it delivered less than three-quarters of first-class post on time in the last year.

Communication Workers Union general secretary Dave Ward said on Wednesday: “We do welcome some of the commitments that have been made but the reality is postal workers across the UK have lost all faith in the senior management of Royal Mail and the service has been deliberately run down.

“We will meet with EP Group next week and call for a complete reset in employee and industrial relations, the restoration of postal services and further commitments on the future of the company.

“We will also be directly engaging with the Labour Party and other stakeholders to call for a new model of ownership for Royal Mail where our members and customers have a direct say in key decisions and the creation of a golden share which will protect a key part of the UK’s communications infrastructure.”