Loss and expense is the money side of employer-caused delay and disruption: the contractor’s entitlement to be reimbursed costs it would not otherwise have incurred, such as extended preliminaries, standing plant and lost productivity.
Unlike an EOT, which moves a date, loss and expense must be proved as actual loss with records: what was spent, why, and how it flows from the event complained of. Global claims that bundle everything together without that linkage are routinely cut down.
Disruption is the hardest head to prove because it is about productivity, not just time. Day-by-day records of gangs, work fronts, access and output are what make a disruption claim measurable rather than rhetorical.
The usual heads are prolongation, disruption, thickening of preliminaries, finance costs and sometimes head office overhead. Prolongation is the most straightforward: the site ran for longer, so time-related costs ran for longer. It still has to be proved with actual cost rather than a rate lifted from the tender, and the period claimed has to match the period of employer-caused delay rather than the total overrun.
Disruption is different in kind. It is the argument that the same work cost more because it was carried out less efficiently: out of sequence, in smaller gangs, in worse conditions, or with constant stopping and starting. Nothing about that shows up as a delay to the completion date, which is why loss and expense and an extension of time are separate claims that can succeed or fail independently.
The evidential burden is higher than most contractors expect. It is rarely enough to show an event occurred and that the job cost more than tendered. The link between the two has to be demonstrated, which usually means comparing planned against actual resource on specific work fronts over specific periods. That comparison is only possible where somebody recorded who was where, doing what, every day.
This is also why the timing of the claim matters commercially. A claim assembled at the end of a job, from invoices and recollection, invites the response that the contractor simply priced the work badly. A claim built from records made as the disruption happened is much harder to characterise that way.
Construction Metric captures that day-by-day resource picture automatically, and its JCT page sets out how the record supports claims under JCT machinery.