European stocks were called to start the day lower on Tuesday tracking Asia overnight, where shares and the euro fell following a warning by credit rating agency Standard and Poor's (S&P) that it could downgrade a swathe of euro zone countries if policymakers fail to reach a deal at a crucial summit on Friday.

The FTSE is called 57 points lower, the DAX in Frankfurt is expected to open down by 68 points and the CAC 40 is called 30 points lower.