An annual Cambridge boat race was brought to a halt after a hammer-wielding man used his boat to block the river in an alleged bid to protect swans.

The man, whose identity is not known, was arrested after causing the Cambridge Christmas Head Race to be delayed by nearly an hour.

Race marshals said the "serial offender" often spreads food for birds along the banks of the river and in the water ahead of races to try to coax them over.

He could be heard shouting about wanting to "protect the swans and ducks" and claimed the rowers would just smash into the birds during the race on Saturday.