Rosberg, who has scored all of his team's 25.5 points so far this year, was a target of Mercedes-powered McLaren two years ago when they were looking for a replacement for double world champion Fernando Alonso but he was bound by his existing contract.

BBC: Rosberg targets switch to McLaren

Another doubted Diamond would become embroiled in the Serious Fraud Office's recently launched Libor probe, even if sources at Barclays confirmed to CNN they are bound by Diamond's contract to cover his legal costs, should he face any.

CNN: STORY HIGHLIGHTS

But American politicians are bound to kick up a stink about any contract going to a firm that has even a vestigial shareholding by foreign governments, albeit allies.

ECONOMIST: EADS and BAE Systems