David Ross, deputy chairman and co-founder of Carphone Warehouse, has resigned from the UK mobile phone retailer’s board after failing to declare he had used most of his shareholding as security for personal loans. Ross also failed to declare similar arrangements at three other companies – National Express, the transport group he chairs; Big Yellow Group, the storage company where he is non-executive director; and Cosalt, the industrial services and leisure products group which he also chairs. He has not resigned from those posts. The failure to disclose the loan arrangements could prove embarrassing for Boris Johnson, the London mayor, who appointed Ross as his representative to the organising committee for the 2012 Olympic Games. The FSA market regulator said directors required clearance from the chairman or chief executive for dealing in shares, which includes using them as security in loans. Possible sanctions for non-disclosure range from private censure to a fine. Carphone said Monday that Ross had disclosed belatedly on Sunday that he had used 136.4m of his shares – or 15% of the company’s equity – as collateral on loans for the past two years.