Did a new identity supplant traditional politics? This study investigates how opinions surrounding Britain's 2016 EU referendum birthed potent 'Brexit' identities.

Using surveys and experiments, we quantify the emergence of this novel affective polarization—directed at those holding opposing Brexit views regardless of party affiliation. Our findings reveal that:

* Prevalence: Brexit identities were widely adopted across the UK electorate.

Personal Significance:* Individuals perceived their own Brexit identity as personally important.

* Cross-cutting Lines: These identities cut through pre-existing traditional party lines.

The research demonstrates this new form of affective polarization rivals that stemming from partisan divides in its intensity, proving political alignment can arise outside conventional parties.