A double-barrelled surname (two surnames joined together, typically with a hyphen) is one of the most popular reasons people use a deed poll in the UK. Whether you are combining your surname with a partner's after marriage, honouring two family lines, or simply preferring the sound of a combined name, a deed poll is the legal instrument that formalises the change. Your marriage certificate will not do this for you; a deed poll is always needed for a double-barrelled name.
Your deed poll states your current full name and the double-barrelled name you are adopting. Once signed by you and two adult witnesses, it is a legally valid document accepted by every major UK organisation: the Passport Office, DVLA, banks, HMRC, the NHS, your employer, and any other body that holds your records.
Both partners in a couple can each use their own deed poll to adopt the same double-barrelled name, creating a shared family name. Say one partner is called Sarah Smith and the other is James Jones, and both can become Smith-Jones or Jones-Smith, each with their own deed poll. The order of the names is your choice; there is no legal convention about which surname comes first.
You do not need to be married, in a civil partnership, or in any relationship at all to create a double-barrelled surname. Any adult in the UK can combine any two surnames for any reason using a deed poll. The names do not need to be your own family names; you can combine any two names you choose, subject only to the general restrictions on name changes (no fraudulent intent, no inherently offensive combinations).
From a practical standpoint, double-barrelled names work well across UK systems. The Passport Office, DVLA, and the major banks all handle hyphenated names without difficulty. You may occasionally encounter older computer systems that struggle with hyphens, but this is an administrative inconvenience, not a legal issue; your deed poll is valid regardless.
If you have children and want to give them the same double-barrelled name, that is a separate child deed poll process. This service generates adult deed polls. For a child's name change, both parents with parental responsibility typically need to consent.