Barclays declined to comment on its ABN plans on Wednesday, but its executives have insisted it is too early to rule on the outcome of the battle.

BBC: NEWS | Business | Share falls weaken Barclays' bid

Among them, the Securities and Exchange Commission last year lost a legal challenge to its plans to empower shareholders to oust underperforming directors, called the "proxy access" rule.

WSJ: Battle Plan Shifts on Dodd-Frank

Facebook has told the BBC that there are currently no plans to merge its services in this way - but did not rule it out from happening in the future.

BBC: Mark Zuckerberg