What does JCT clause 4.22 mean?

Clause 4.22 of SBC/Q 2016 is the list of Relevant Matters, the events for which the Contractor may recover direct loss and expense under clause 4.20 when they materially affect regular progress; nothing outside the list qualifies, however much it cost. The list is short. Variations, including anything the contract treats as a Variation, are the first and the commonest. Instructions of the Architect/Contract Administrator under the clauses the list names are the second, including postponement of work and opening up or testing where the work proves to be in accordance with the contract so the cost is not the Contractor's. Deferment of giving possession of the site under clause 2.5 is the third, where the Contract Particulars allow it. The fourth is an approximate quantity in the Contract Bills that turns out not to be a reasonably accurate forecast of the quantity of work required. The fifth is suspension by the Contractor under clause 4.13 for non-payment. The sixth is any impediment, prevention or default, by act or omission, of the Employer or of the Employer's Persons, except to the extent caused or contributed to by the Contractor or the Contractor's Persons. That last item is the catch-all and is where most argument sits, because it requires the Contractor to show the act or omission, the Employer's responsibility for it and the effect on progress. The Relevant Matters are a money list only; the events that ground an extension of time sit in the separate extension of time provisions, overlap with this list but are not the same as it, and the practice does not assess time. What goes wrong is claiming for an event that is not on the list, such as weather or a subcontractor's failure, treating an extension of time as proof of a Relevant Matter, and failing to tie each pound of loss to a named item on the list.