Britain ramped up a Brexit space row with the EU on Thursday, saying it will demand repayment if it is excluded from the Galileo satellite navigation project.
Newspaper reports suggested London could seek £1 billion ($1.34 billion, 1.14 billion euros) in compensation for its investment in the programme.
Brussels has said it will deny London access to Galileo's encrypted signals after Brexit, citing legal issues about sharing sensitive security information with a non-member state.
A report issued by Britain's Department for Exiting the European Union said it had "strong objections" to being frozen out of the 10-billion-euro programme and called for an "urgent resolution to the exclusion".
"Should the UK's future access be restricted, the UK's past contribution to the financing of space assets should be discussed," the report said.
The British report suggested it may have to reopen negotiations on the £39 billion (40-45 billion euros) Brexit "divorce bill" that was agreed in December to make up for its exclusion.
It said the deal agreed then had provided for Britain's continued involvement in the Galileo programme, which has important uses in both the civilian and military fields.
Talks in Brussels this week on resolving the issue had failed to make headway with "big gaps" remaining between the two sides, sources said.
- 'German-backed clique' -
Freezing Britain out of Galileo could delay the programme by three years and cost the EU a further one billion euros in development costs, British sources said.
London has warned that being excluded could have implications for the its future defence partnership with the EU.
"Negotiations on the future partnership should not be preempted or prejudiced," it said.
The European Commission said its position was "very very clear, crystal clear" about why Britain was being excluded.
"This issue is being discussed with our British partners, negotiations are ongoing," commission spokesman Margaritis Schinas told a daily briefing.
Britain played a major role in developing Galileo, an alternative to the US's GPS, which is expected to be fully operational in 2026.
It demands continued British access to the secure signal and a right to compete for contracts.
Britain is looking into developing its own, separate system if the EU maintains its position, and has also raised the question of Galileo's use of Britain's overseas territories as monitoring bases.
The Times newspaper reported Thursday that the decision to block Britain was being led by a "German-backed clique" in the European Commission, and that it had caused a rift with French officials, who were reportedly unhappy with the plan.
Spain, Sweden, the Netherlands and the Baltic states have also objected to denying Britain access, said the report.