The Brexit row between the UK and the EU-27 over Galileo is escalating. Britain's space agency has written to 13 firms to remind them that they need security authorisation to engage in any future contracts on the sat-nav system.
It is being interpreted as a threat to block UK tech developed for Galileo from being transferred into the EU-27. The European Commission says Brexit means the UK will have to be excluded from a key element of the system after March next year.
This is the Public Regulated Service, or PRS - a navigation and timing signal intended for use by government agencies, armed forces and "blue light" services. The PRS is designed to be available and robust even in times of crisis.
Brussels says London cannot immediately have access to it when the UK leaves the European bloc because it will become a foreign entity. PRS is for EU member states only.
The European Commission has also made it clear that British companies will not be allowed to work on PRS after Brexit.
London's dismay at being shut out of a system it helped develop has been to raise the prospect of withdrawing from Galileo completely, and to consider starting up its own indigenous sat-nav network. Such a move could slow the development of Galileo - which is not yet complete - and increase its costs.