The sale of the Royal Mail to Czech billionaire Daniel Kretinsky’s EP Group is close to completion and could be confirmed in the next two weeks, according to sources close to the deal.

Kretinsky has agreed to make further concessions to achieve the takeover, the BBC understands.

The unions held meetings with Kretinsky’s advisers this week, and while some sources say they are “wary” about it, the Communications Workers’ Union (CWU) said meetings with the EP Group were “constructive”.

The deal is still subject to approval under the National Security and Insurance Act although officials stood in for a similar review when he increased his stake in the company.

Mr Kretinsky’s EP Group declined to comment.

The entrepreneur has already offered the following guarantees to get the deal:

• “One price goes anywhere” maintaining a universal service and not raiding the pension surplus
• Retaining the Royal Mail brand name and headquarters and tax residency in the UK for the next five years
• Respect union demands without making any compulsory redundancies (until 2025)
• Negotiate with the CWU to extend that promise of jobs

The board of Royal Mail’s owner, International Distribution Services (IDS), has proposed the £3.6bn offer price to its shareholders and is expected to accept a sufficient number, allowing the deal to go ahead.

It is thought that additional safeguards could be included to extend the duration of the guarantees it offered.

The BBC understands that they are sufficient to satisfy the UK government that Daniel Kretinsky is a suitable owner for this historic and important organisation.

Speaking before MPs on Tuesday, Business Secretary Jonathan Reynolds referred to him as a “legitimate business figure” whose alleged links to Russia had already been reviewed and dismissed when he became the company’s largest shareholder.

A spokesman for the CWU said meetings so far with the EP Group had been “frank and constructive and will continue in the coming days”.

Royal Mail, which was split from the Post Office and privatized ten years ago, has a legal duty to deliver a one-price “universal service”, meaning it must deliver letters six days a week, Monday to Saturday, and parcels from Monday to Friday.

But the company’s performance has deteriorated in recent years, leading to heavy financial losses.

Customers have also complained about deliveries, with important medical appointments and legal documents not being delivered on time.

The number of letters being posted in the UK has also fallen, with half the number being sent compared to 2011 levels.

Meanwhile, parcel delivery is becoming more popular – and more profitable.

Parent company IDS made a small profit last year generated entirely by its logistics and parcel business in Germany and Canada, offsetting losses at Royal Mail.

The universal service obligation is currently under review, with Royal Mail proposing to regulator Ofcom that moving second class deliveries to every other day of the week would save up to £300m a year and give the business.

In an interview with the BBC earlier this year, Kretinsky said that “as long as I live” he would respect the universal service obligation – but he favored the reforms proposed by the Royal Mail.

The Business Department was also contacted for comment.