Can I stick in some thoughts on the consideration issue, from a practical perspective?

Renegotiation of contracts is a fact of commercial life. In any individually negotiated contract of much complexity or duration, it is probably the norm, not the exception. Sometimes it is genuinely bilateral (as is often the case with long-term contracts). But often it is driven by pressure from one side, which effectively seeks a revision of the contract in its favour.

Such cases fall on a spectrum. At one end, there are clear or thinly disguised cases of extortion: the party-obliged-to-peform (“POP”) refuses to do so unless the party-entitled-to-performance (“PEP”) sweetens the deal. Although, in theory, PEP could simply refuse to cave in, it will often seem better to capitulate, because remedies for breach of contract are expensive, partial, and often pointless. At the other end are cases where there has been some change of circumstance which at least teeters on the brink of justifying POP’s refusal (arguable frustration, for instance). In the big middle area are the many cases where POP has no contractual leg to stand on, because it is the victim of a risk that in contractual terms it took (as in MWB v Rock, or Williams v Roffey). But in practical terms it is often in PEP’s interest to give some ground if that will actually lead to (approximate) performance.

Where people do reach a deal on these things, there are usually sound practical reasons to make the PEP stick to its word. That is, I'm sure, what most people in the commercial world expect. Encouraging debtors who are in trouble to deal openly with their creditors, rescheduling debt and so forth, is generally a good thing. And once an agreement is made, POPs will often rely on it, for instance in deciding to carry on trading rather than entering some insolvency process; but that decision may affect not only them but other creditors, employees, suppliers and so forth. Still, there remains a residual concern that unscrupulous POPs, those at the extortion end, don’t really deserve such treatment

The trouble is that contract law provides no sufficiently specialised tool to deal with the distinction we might want to make between the many cases where such agreements should be respected, and those where we are inclined to allow the PEP to back out.

Consideration doesn’t do it. In many simple cases it should render the renegotiation unenforceable. But whether it does so or not is largely adventitious, and it is easy to work around. There are any number of avoidance devices, from tom-tits and peppercorns or some other commercially irrelevant variation in POP’s or PEP’s obligation, to “mutual cancellation and re-contract”, to somewhat contrived “disputes” that can then be settled, or if all else fails a deed. They are all essentially formal devices, as usable by the unscrupulous as the scrupulous. No properly advised person will ever fail to make a variation effective if they try even slightly. Quite often even the not-properly-advised will manage to do it by luck. Whatever it does, it never nicely tracks the things that really seem relevant.

It doesn’t seem to me that the “practical benefit” reworking helps much. I suspect it is used as a conveniently incomprehensible way to triage these cases, but it’s intellectually dishonest because there is almost always a practical benefit, since if there wasn’t the PEP wouldn’t make the deal at all. Even not having to sue someone (yet!) is, as anyone who ever has will attest, a win of sorts. That may explain why in the cases the judges struggle to find some benefit other than the mere fact the PEP may not have to sue for performance, but this leads to some odd reasoning, where the elephant goes unexamined while all attention focuses on some mouse in the corner.

Really consideration seems like a sort of weird appendage, a vast structure which in the end does nothing much more than make parol contracts to make gifts unenforceable and intermittently play up so as to make a variation fail. (And no, except to dyed-in-the-wool formalist, an agreed variation is not a contract to make a gift!)

Economic duress seems superficially more promising, but (quite apart from being a conceptual mess in its own right) it doesn’t help either because it is a necessarily narrow doctrine, and it isn’t much good for a well-heeled PEP faced with an affordable but totally unjustified demand by an unscrupulous POP. Expanding it would give rise to a great deal of trouble. If we had a proper doctrine of good faith, that might help; but of course it has other problems too, especially of uncertainty.

The truly rigorous positions would be (i) to insist that no variation is permissible unless it is truly bilateral (which, to be really effective, would require expanding the doctrine of consideration so that it looked at substance not form: a bad move) or (ii) to insist that all seriously intended variations are enforceable, subject to duress (and perhaps some doctrine of good faith), if necessary as a (further) exception to the requirement for consideration. If I had to choose, I’d pick the latter, because the former moves the law still further than it already is from the ordinary expectations of honest commercial people. But UKSC may prefer to stick with the current messy and incoherent approach, in some ways not despite its messiness and incoherence but because its messiness and incoherence allows an element of case-specific discrimination, albeit concealed, and it pays at least lip-service to orthodoxy. I'm sorry to say that I expect the vestigial tail to go on twitching, if not wagging. I hope I'm wrong.