The Maritime and Coastguard Agency launched an investigation into the first spill, but has since said it had been unable to trace the source of the pollution and confirmed it had closed the investigation.

BBC: 'Sticky substance' birds rescued in Devon and Cornwall

Mr Hall said the senior police source also confirmed that ropes and forensic-style overalls were found on the men.

BBC: Pair held over Joss Stone robbery plot in Devon

An unnamed Syrian security source confirmed the army chief's defection but played down its significance, Reuters news agency reports.

BBC: Syria crisis: Military police chief al-Shalal defects