Does an expired certificate mean the policy has lapsed?

Not necessarily. Certificates are collected once and policies renew independently of any single project, so an expired certificate is common and often just means nobody has requested the new one yet. Confirm with a current document rather than assuming either way.

Can work continue while a new certificate is being chased?

That depends on the contract. Some insurance clauses make current evidence of cover a condition of continuing to engage a subcontractor, in which case it is the principal’s or head contractor’s call, not an assumption to make informally.

What if the subcontractor cannot produce a current certificate at all?

Treat that as a live gap, not a delay. Ask directly whether cover is currently in force, in writing, and do not rely on the previous certificate as evidence of anything beyond the period it actually states.

A certificate that has expired mid-contract

In short

An expired certificate is a paperwork gap, not proof the policy has lapsed. The two are frequently the same thing, but they are not automatically the same thing.
The fastest fix is asking whoever arranged the policy for a current certificate covering today’s date. If the policy renewed on the same terms, this is quick.
If the policy did not renew, or renewed with a gap, that is a different and more serious problem, and it needs to be found out immediately rather than assumed away.

A subcontractor is midway through a job when someone checks the file and finds the certificate of currency on record shows a period that ended weeks ago. The work is ongoing. The question is whether there is actually a coverage gap, or just an out-of-date piece of paper.

Those are different problems with different urgency, and the only way to tell them apart is to ask.

Why this happens

Certificates are tied to a period of insurance, and most business policies renew on a set date each year, independent of any particular project’s timeline. A certificate collected at the start of a long job will routinely fall outside its stated period before the job finishes.

That is expected and, on its own, not alarming — it happens on almost every project that runs longer than a policy year. What matters is whether the policy actually renewed.

What to ask, immediately

Ask the party who holds the policy — directly, not through a chain of subcontracts — for a current certificate showing today’s date within the period stated. Ask them to confirm whether the renewal was on the same terms, or whether anything changed.

Do not accept an assurance in place of the document. "It renewed, don’t worry about it" is not evidence; a certificate with a current period is.

If the policy genuinely lapsed

If the policy did not renew, or renewed with a break in between, there has been a real gap in cover — potentially including the period the work has continued during. That is a materially different situation from an administrative delay in sending a new certificate.

Where a subcontractor insurance warranty is part of the contract, continuing to engage a business whose cover has actually lapsed is the exact scenario that warranty exists to catch. Escalate it as a contract issue, not just a paperwork one.

Why the warranty makes a lapse your problem too

Questions

Does an expired certificate mean the policy has lapsed?: Not necessarily. Certificates are collected once and policies renew independently of any single project, so an expired certificate is common and often just means nobody has requested the new one yet. Confirm with a current document rather than assuming either way.
Can work continue while a new certificate is being chased?: That depends on the contract. Some insurance clauses make current evidence of cover a condition of continuing to engage a subcontractor, in which case it is the principal’s or head contractor’s call, not an assumption to make informally.
What if the subcontractor cannot produce a current certificate at all?: Treat that as a live gap, not a delay. Ask directly whether cover is currently in force, in writing, and do not rely on the previous certificate as evidence of anything beyond the period it actually states.

Sources

ASIC — Regulator of the AFS licensees and authorised representatives — including brokers — who issue certificates of currency.
business.gov.au — business insurance — Australian Government guidance on business insurance types and managing cover.