Is an electronic signature legally valid in the UK?

Short answer: for most commercial contracts in England and Wales, yes. English law generally does not require a particular form of signature, and the courts have accepted electronic signatures of many kinds. There are important exceptions, set out below. This page is general information, not legal advice. For a specific document, check the rules that apply to it or ask a solicitor.

Where validity comes from

Validity comes mainly from the common law: a signature is valid when the person intends to authenticate the document, whatever its form, unless a statute or the parties require something more. This is the conclusion of the Law Commission in "Electronic execution of documents" (Law Com No 386, September 2019). The Government accepted that statement of the law in a ministerial statement on 3 March 2020.
UK eIDAS, Article 25(1) (Regulation (EU) No 910/2014 as retained in UK law): an electronic signature must not be denied legal effect or admissibility as evidence in legal proceedings solely because it is electronic, or because it does not meet the requirements for qualified electronic signatures.
Electronic Communications Act 2000, section 7 deals with admissibility: an electronic signature, and its certification, is admissible in evidence on the authenticity or integrity of a communication or data. It does not by itself make a signature valid.
Whether a particular signature was made by a particular person, and how much weight the evidence carries, is for the court to decide. The certificate of completion and the audit trail help with that evidence; they do not replace it.

What Kairos-K Sign provides

A simple electronic signature (UK eIDAS Article 3(10)). Each recipient:

proves control of their email address with a one-time code (optionally also a phone number by SMS code);
agrees to sign electronically;
adopts a signature;
presses "Sign" next to a statement of exactly what they sign.

The completed PDF carries a certificate of completion: who, when, IP address, browser, the fingerprints of every document and an audit trail. It also carries an electronic seal and, when configured, a trusted timestamp; these show any later change to the file.

It is not an advanced or qualified electronic signature. It does not check identity beyond control of an email address (and phone, if used). It has no witnessing process.

About the seal. While the seal uses a self-signed certificate, PDF readers such as Adobe Acrobat show the signature validity as "unknown", because the certificate is not on their trusted list. They still show whether the file was changed after sealing. Once a publicly trusted (AATL) certificate is installed, the reader shows the seal as valid.

Documents this service is not suitable for

Deeds signed by individuals must be signed in the presence of a witness who attests the signature (Law of Property (Miscellaneous Provisions) Act 1989, section 1(3)). The Law Commission's view is that the witness must be physically present. Kairos-K Sign has no witnessing flow, so do not use it for deeds signed by individuals.
Documents executed by a company (Companies Act 2006):
- A company can make a contract through any person acting under its authority (section 43). A simple contract signed for a company by an authorised person through this service is usually fine.
- To execute a document (section 44), a company uses its common seal, or the document is signed by two authorised signatories (two directors, or a director and the company secretary), or by one director in the presence of a witness who attests the signature.
- Two authorised signatories can each sign electronically, without a witness, in separate steps of one envelope.
- A single director signing with a witness needs the witness to be physically present, which this service does not support.
- A document executed as a deed must also be delivered as a deed (section 46).
- The automatic countersignature of Kairos-K Sign is never used for documents marked as a deed or as needing a witness, or for documents to be executed under section 44.
HM Land Registry: dispositions to be registered must follow Practice Guide 82, which accepts electronic signatures only through its own process with a conveyancer. Kairos-K Sign does not meet the requirements of Practice Guide 82. Do not use it for transfers, charges or other documents for registration.
Wills must be signed in wet ink, in the presence of two witnesses who are present at the same time (Wills Act 1837, section 9). Do not use this service for wills or codicils.
Lasting powers of attorney and other documents with prescribed forms or processes: follow the process of the body that receives them (for example the Office of the Public Guardian).
Documents that must carry an advanced or qualified electronic signature, and documents for courts, regulators or use abroad that have their own requirements: check before sending.

Practical tips

For engagement letters, service and agency agreements, NDAs, consents and internal approvals, a simple electronic signature with a good audit trail is usually enough.
Where you need stronger proof of identity (for example under anti-money-laundering rules), check identity separately and keep that evidence. Link it to the envelope with a client reference.
Keep the completed PDF and the certificate. For a dispute, download the evidence pack from the envelope page.

Sources

Version: draft-2026-10-24