(ShareCast News) - Insurance group Legal & General has agreed a mandate to manage £13bn of assets for the National Grid UK Pension Scheme.The FTSE 100 group said the scheme will create a small executive office of pension and investment specialists to support the trustees in the management of the £17bn fund's assets.Legal & General, who also announced the acquisition of Aerion Fund Management, the in-house manager of the scheme, said it will provide portfolio solutions to the trustees through the executive office, which will determine the strategic asset allocation and provide oversight of external managers.The London-listed group added it expects to complete the transaction before the end of the year.Legal & General were down 0.39% to 253.70p at 1457 BST on Friday.