Do British Pagans believe they have a special or exclusive connection with the ancient dead of British provenance?

The answer is very simply no - Pagans make no claim to have a special or exclusive connection with the ancient dead. This question is another that expresses a misunderstanding about the Pagan perspective, and indeed one that is wholly irrational.

The Pagans HAD represents are Britons. In terms of genetics, the vast majority of Britons are just as likely to be descended from the ancient dead (and most of us are) whether or not they are Pagan. Equally importantly, most Britons feel a special connection to bodies exhumed in their local environment, however old those remains are. Far from detracting from HAD's argument, this backs their case.

For the Pagan, however, the connection can be a little deeper. In most Paganisms there is an integral connection with the past, both in terms of landscape and those who lived upon it. The value of heritage, from pre-history to modern cultural expression, is woven into Pagan beliefs and practice. In other words, heritage is not a secular but an overtly religious / spiritual part of Paganism. Needless to say, this includes the remains of the dead.

As such, practising Paganism doesn't provide a special or exclusive connection. What it does create is a particular perspective about human remains that is spiritually, emotionally, viscerally experienced as connection, and that connection is a foundation to much Pagan religious / spiritual practice.