The two are confused constantly, including by people who have signed both, and the confusion runs in the direction that hurts. Collateral is a thing: a specific asset, identified in the documents, valued, and charged to the lender, who holds a right over it before anything goes wrong. A personal guarantee is a promise: a written undertaking by an individual, usually a director, to repay the company’s borrowing personally if the company does not. Nothing is charged. Nothing is valued. No asset is named.
Which is why a facility carrying one is still called unsecured, and why that word misleads. The absence of security describes the lender’s position over assets, not who is on the hook. Most SME facilities here carry a guarantee from one or more directors, because it is what gives a lender recourse when there is no asset to look to. A director who reads “unsecured” as “nothing of mine is at stake” has misread the most consequential document they will sign.
The difference shows when something goes wrong. With collateral, the lender enforces against the named asset: the route is pre-agreed, the target known, and once the asset is realised the exposure falls by whatever it fetched. With a guarantee there is no named target — the lender has a claim against a person, pursued through the ordinary recovery process, reaching that person’s assets and income generally. Less predictable, and not confined to anything you decided in advance to risk.
Treat the guarantee as a negotiable term. Its existence often is not; its shape frequently is. Whether liability is capped at an amount, whether it covers this facility only or all present and future liabilities, whether it is joint and several so that one director can be pursued for the whole, and what event releases it. Those terms live in the facility letter, and anything agreed verbally that is not written there does not exist.