The UT, essentially, held that, given the very limited rights attaching to the special LLP interests, their sale was not a capital transaction. It then went on to consider the MMP rules.
For the MMP rules to apply, broadly, either the corporate member must have received an individual member's "deferred profit" or the individual must have the "power to enjoy" the corporate member's profit share. The UT (following the FTT) gave these conditions a wide (i.e. HMRC-friendly) reading, and concluded that they were both met. However, crucially, unlike the FTT, it held that a further requirement, the "counterfactual test", was satisfied.
The "counterfactual test", broadly, requires that it is reasonable to suppose that by virtue of the individual's deferred profit being allocated to the corporate member or the individual's "power to enjoy", both (i) the individual's profit share, and (ii) the individual's and corporate member's aggregate tax liability, are less than they otherwise would have been.
In essence, the FTT had held that, as the remuneration structure was part of a global Boston Consulting Group programme that was implemented (in different ways) worldwide, even if the specific LLP arrangements had not existed, the individuals would still not have received the 18%. Instead, a different commercially-similar structure would have been implemented. Therefore, the counterfactual test was not met. However, the UT took a different approach.
The UT held that it was not right to speculate on how the global business would have implemented the remuneration structure in the UK differently. Rather, all the LLP's profits have to be allocated somewhere, and if the 18% had not been allocated to BCG Ltd, it is reasonable to assume that it would have been allocated to the individuals.
For good measure, the UT confirmed that the miscellaneous income tax charge applied to payments received in tax years before the MMR rules were introduced, and that if it were wrong in relation to the MMP rules and/or miscellaneous income rules, the sales of occupation income rules would apply.