Documents show the concerns held by the Financial Services Authority about the ability of Barclays to maintain a big enough capital cushion if it proceeded with the takeover of Lehman Brothers A series of intense transatlantic phone calls between US and UK regulators made during the frantic weekend that ended with the collapse of Lehman Brothers are detailed in the Financial Services Authority’s first documented account of the bank’s demise. The account is based on confidential information it would normally not have been able to disclose. While the FSA chief executive Hector Sants refused to give evidence in person to a court-appointed US bankruptcy examiner , the regulator submitted written evidence which shows the US authorities made repeated attempts to convince the UK to change its rules to make it easier for Barclays to take over the ailing US bank