Does it affect subrogation rights if the guarantor is a voluntary guarantor (ie the borrower did not procure, or even know about, the existence of the guarantee)?

Subrogation

The expression 'subrogation' is a convenient way of describing a transfer of rights from one person to another, without assignment or assent of the person from whom the rights are transferred and which takes place by operation of law in a whole variety of widely different circumstances. For more information, see: Doctrine of subrogation: Halsbury's Laws of England, Equitable Jurisdiction vol 47, (2021), para 208.

A guarantor's right to subrogation of the lender's rights

As a general rule, once a guarantor has paid the debt which has been guaranteed in full, it is entitled to be subrogated to all of the guaranteed party's rights against the principal in respect of the debt which has been guaranteed. The authority for this is section 5 of Mercantile Law Amendment Act 1856 (MLAA 1856), which provides that:

‘Every person who, being surety for the debt or duty of another, or