no public sector investment as imposed by the EU

Do you know in what way this is actually stated, in what regulation, what law, what directive, or so on?

Or, at any rate, their interpretation by the European Commission.

As a first step, it has to determine whether a company has received State aid, which is the case if the support meets the following criteria:

• there has been an intervention by the State or through State resources which can take a variety of forms (e.g. grants, interest and tax reliefs, guarantees, government holdings of all or part of a company, or the provision of goods and services on preferential terms, etc.);
  
• the intervention confers an advantage to the recipient on a selective basis, for example to specific companies or sectors of the industry, or to companies located in specific regions;
  
• competition has been or may be distorted;
  
• the intervention is likely to affect trade between Member States.

By contrast, general measures are not regarded as State aid because they are not selective and apply to all companies regardless of their size, location or sector. Examples include general taxation measures or employment legislation.