No is the short answer. With the limited number of graves from people who died back then, it's not possible to say regular sacrifices were carried out. Anecdotal evidence suggests sacrifice was a thing well known - Lindow man was certainly ritually killed, there are the stories of sacrifices to Crom Cruach in Ireland which while not necessarily Brythonic are a culturally close people. We barely know anything about Brythonic shipping yet at some point large clinker built ships carried trade goods between the British Isles and the Continent and also trade within British waters. So far though there is an absence of the ritual centres that existed in Gaul where the remains of enemies were put on display though whether those were ritually killed or died in battle is hard to say. The absence of a head for a trophy closet doesn't mean the headless body was ritually sacrificed.