Just looking at the link, it appears that the opening comment:
but for a mere 1 Billion GBP we could save 1 Billion GBP a day.
It appears that that line should be that for 10 Billion GBP we could save 1 Billion GBP per year.
And whether we will need this option is still open to debate/negotiation:
The European Union has indicated that UK firms may, be barred from bidding for contracts on its Galileo programme on security grounds, while British armed forces and emergency services could be denied access to encrypted signals.

So the PM is getting prepared for a 'worst case' scenario. This seems a sensible move. If it goes ahead the plan is to have a UK system launched by the 'mid 2020s'. As opposed to galileo, which is due to be fully functional by 2026.