[theluketaylor]

Not an expert on the UK, but here in Canada common law marriage is absolutely a thing. Just filled in my 2021 census yesterday and one of the selectable marital status was "common law" and many government documents refer to the status. Common law relationships are generally much easier to dissolve, but courts have held them as strong as legal marriages, especially if the relationship lasts decades and includes children. They form without any specific action beyond time spent living together.

property on dissolving: https://www.ontario.ca/page/dividing-property-when-marriage-...

employment benefits must extend to common law partners: https://www.ontario.ca/document/your-guide-employment-standa...