Lord Neuberger, the President of the Supreme Court, gave the leading judgment and highlighted that the weight given to statements made in other documents available at the time of the contract in question must be “highly dependent on the facts of the particular case”. However, in cases of contracts documenting the terms on which a negotiable instrument are held, he stressed that “very considerable circumspection is appropriate before the contents of such other documents are taken into account”.
The starting point, therefore, for construing such debt instruments is the often cited approach adopted by the House of Lords in In re Sigma Finance Corp (in administrative receivership)  UKSC 2. In that case, Lord Collins observed that, where a trust deed concerned securities issued to “a variety of creditors, who hold different instruments, issued at different times and in different circumstances”, the background or matrix of fact could only be of very restricted relevance in exercises of contractual construction.
In departing from this general principle, however, Lord Neuberger later remarked that, in the Bank’s case, the Trust Deed and the relevant redemption provisions could not reasonably or properly be understood unless “one has some appreciation of the regulatory policy of the FSA at and before the time the ECNs were issued”. This chimes with Lady Justice Gloster’s judgment in the Court of Appeal that the 'reasonable addressee' of the Exchange Offer Memorandum had to be taken as “someone having an informed understanding, whether on his own or with the assistance of a financial adviser, of the working of the relevant markets, the regulatory background, the use of stress tests in the regulator’s testing of the adequacy of a bank’s capital resources and the function which the ECNs were intended to fulfil”.
Having therefore decided to admit the regulator’s statements to the relevant factual matrix (along with the other documents referred to above), the next question for the Court was whether the ECNs, in order to be “taken into account”, had to play some part in enabling the Bank to pass the stress test as opposed to merely being theoretically taken into account for some purpose in the stress test. In agreeing with the Court of Appeal's approach, Lord Neuberger said that the vital consideration was that, under the new capital adequacy regime, the ECNs could not fulfil the job for which they were designed, i.e. to convert to shares before the relevant ratio was reached. He also remarked that the wording of the clause itself suggested that the words “taken into account” more naturally connoted a dependence upon practical developments than requiring a disallowance in principle before it could cease to apply.