SES, AES and QES: the three types of electronic signature
UK eIDAS defines three levels of electronic signature. Each level adds requirements about identifying the signer and protecting the document. All three are legally valid; they differ in how much they prove on their own.
The three types at a glance
| Type | What UK eIDAS requires | Typical use |
|---|---|---|
| SES Simple | Data in electronic form, attached to or associated with the document, that the signer uses to sign. | Most business documents: contracts, engagement letters, client care letters, tenancy agreements. |
| AES Advanced | Uniquely linked to and capable of identifying the signer; under their sole control; linked to the document so any later change is detectable. | Higher-value or higher-risk documents, or where the signer’s identity must be verified. |
| QES Qualified | An AES based on a qualified certificate from a qualified trust service provider, made with a qualified signature creation device. | Where a law or the other party specifically requires it, often in cross-border dealings. |
Simple Electronic Signature (SES)
UK eIDAS defines an electronic signature broadly: data in electronic form attached to or logically associated with other data, which the signer uses to sign. A typed name, a signature drawn on a screen and a click on “Sign” can all qualify.
An SES is legally valid. UK eIDAS says a signature cannot be denied legal effect just because it is electronic or is not qualified. What an SES does not do by itself is prove who signed, so its strength depends on the evidence around it: how the signer was checked, and whether the document can be shown to be unchanged.
Advanced Electronic Signature (AES)
Article 26 of UK eIDAS sets four requirements. An advanced signature must be:
- uniquely linked to the signer;
- capable of identifying the signer;
- created using signature-creation data the signer can, with a high level of confidence, use under their sole control;
- linked to the signed data so that any later change to it is detectable.
In practice, the first two mean verifying who the signer is, typically with an identity check against a government document, rather than relying only on access to an email inbox.
Qualified Electronic Signature (QES)
A qualified signature is an advanced signature that is also based on a qualified certificate, issued by a qualified trust service provider, and created with a qualified signature creation device. It is the only type that automatically has the same legal effect as a handwritten signature.
Few UK documents legally require a QES. Since Brexit, the UK and the EU keep separate lists of qualified trust service providers, so if a counterparty asks for a qualified signature, check which list they mean.
Choosing the right type
- Start from the document. If no law, regulator or contract asks for a particular type, an SES is valid.
- Think about the dispute you want to win. The weaker the link between the signer and their email address, the more an identity check is worth.
- Check special cases. Wills, deeds and documents for registration have their own rules; see our guide to UK e-signature law.
Where Pactivo fits
Pactivo provides Simple Electronic Signatures under UK eIDAS today, built to carry stronger evidence than a bare SES: every signer clears a one-time passcode sent to their email before the document opens, every event goes into a hash-chained audit trail, and the finished PDF is sealed with a PAdES digital signature and an RFC 3161 timestamp. Advanced signatures with identity verification, and Qualified signatures, are on our roadmap; the trust centre has the current position.
This page explains the general position in plain English. It is not legal advice; for a decision about a specific document, take advice from a solicitor.