The recent Scottish case of SGL Carbon Fibres Ltd v RBG Ltd  has reiterated the established principle of “he who avers must prove”. RBG Ltd were employed by SGL to carry out engineering works at their premises in Scotland under the NEC3 Option C form of engineering and construction contract. A dispute arose between the parties concerning an alleged over-payment by SGL to RBG. Section 5 of the NEC is, of course, silent on the question of over-payment and simply sets out the payment procedures. However, the employer insisted that, notwithstanding this, the contractor was obliged to “own up” and justify the alleged over-payment it had received and repay the money. The contractor rejected this and the matter went to an arbitrator who found in favour of the contractor. The Outer House of the Scottish Court of Session then rejected an appeal by the employer against the arbitrator’s decision. Lord Glennie found that the burden of proof in this case lay with the employer to prove that any sums paid to the contractor amounted to overpayment, in the same way that the contractor bore the burden when seeking additional payment over and above what was certified. Whilst Lord Glennie’s opinion is not binding on the English courts, this judgement will be useful in informing any arbitrator or adjudicator dealing with a similar payment dispute under NEC 3.