European leaders will discuss how to combat aggressive tax avoidance by major companies such as Amazon, Google and Apple at a summit on Wednesday, and cut the estimated Euro 1 trillion a year the EU loses to tax evasion or avoidance.The four-hour summit was originally called to discuss energy policy, but investigations in Britain, France and the US exposing how little tax major international companies have been paying by carefully structuring their European operations has forced the issue to the top of the agenda.