In the Belgian threads threads its often written that if you use a UK company for work in Belgium, it might be decided that the UK company should be taxed like a Belgian company.

Is this based on weather the turnover is Belgian, or is it OK if for example 70% goes to Belgian salary, subcontractors, expenses?

What should you do to "be safe"?

Is it a problem only from the foreign side?
Are the rules much the same from country to country?

Does it have other consequences than having to pay the tax you should have paid anyway?