It's possible to switch from owning a property on a joint tenants basis to a tenants in common basis and vice versa.
There are various reasons for wanting to switch. Perhaps there's been a change in the relationship between you and your joint owner, or possibly there's somebody else you'd prefer to inherit your share of the property.
'Severance of a joint tenancy' refers to the process of switching specifically from joint tenants to tenants in common. Unlike switching from tenants in common to joint tenants, where you need everyone's agreement, you don't need everyone's agreement to switch from joint tenants to tenants in common.
If you're considering switching tenancy arrangement but aren't sure it's the right decision, it's worth seeking legal advice. For more details, including how to start the process of severing a joint tenancy, see Gov.uk