“Two conditions must be satisfied: first, there must be a clear mistake on the face of the instrument; secondly, it must be clear what correction ought to be made in order to cure the mistake. If those conditions are satisfied, then the correction is made as a matter of construction.” 23. Subject to two qualifications, both of which are explained by Carnwath LJ in his admirable judgment in KPMG LLP v Network Rail Infrastructure Ltd [2007] Bus LR 1336, I would accept this statement, which is in my opinion no more than an expression of the common sense view that we do not readily accept that people have made mistakes in formal documents. The first qualification is that “correction of mistakes by construction” is not a separate branch of the law, a summary version of an action for rectification. As Carnwath LJ said (at p. 1351, para 50): “Both in the judgment, and in the arguments before us, there was a tendency to deal separately with correction of mistakes and construing the paragraph ‘as it stands’, as though they were distinct exercises. In my view, they are simply aspects of the single task of interpreting the agreement in its context, in order to get as close as possible to the meaning which the parties intended.” 24. The second qualification concerns the words “on the face of the instrument”