Restricted sources and organisations. LOL. Someone is trying to make this sound more exciting than it really is.
Technically, mobile phone signal repeaters/boosters have always been illegal in the UK without a licence. However, the law wasn't very clear, and people selling mobile phone boosters would argue that they were legal, as all you had to do was make sure that it didn't cause interference. Indeed, many people have been using them for many years with no issues, both in-car systems like the phone box, or building systems for homes in remote areas. In general, with correctly installed and designed systems there have been very few problems, and the authorities were not particularly interested in the issue.
In August of last year, OFCOM announced that they were investigating the issue of mobile phone signal repeaters and said that they intended to legalise the use of low-power mobile phone boosters, such as in-car systems, so that they could be used without the need for a licence.
At the end of March 2018, OFCOM announced that they were making the use of in-car mobile phone repeaters legal.
The problem, however, was the small print. In order to be legal, an in-car booster needs to be an extremely sophisticated device, almost as complex as an entire phone, rather than just an off-the-shelf signal booster circuit. Even the most sophisticated repeaters on the market designed for things like cruise ships with thousands of guests do not have systems as advanced as that which OFCOM are requiring for an in-car system.
The problem is that now that OFCOM has specifically said that things like the phone box are illegal without a licence, companies like Audi/VW have little choice but to comply with the law by stopping to sell these things, or redesign them (however, given that this is a UK only requirement, and the cost of the technology required is substantial, the mobile phone box may need to become a significantly more expensive option).
