US and European sanctions against Moscow pose a threat to Western economies, according to the former boss of oil major BP.Tony Hayward, now chief executive of General Eenergy and chairman of Glencore, has said that measures - which include cutting off Russian energy groups' access to capital markets and depriving them of Western oil technology - could constrain oil supply and push up prices.In an interview with the Financial Times, Hayward said that the restrictions would leave the global economy exposed to possible volatility in the flow of oil.He said that markets have been "lulled into a false sence of securitiy" by the recent shale boom in the US, which has driven crude output up 60% since 2008."When US supply peaks, where will the new supply come from?" Hayward asked.He reckons that "the big gorillas are going to start cutting their activities" as a result of Western sanctions, which threaten production in the Artic and Siberia.