The crime was not new.
It was high treason as defined by the Statute of Edward the Third.

The punishment was not new.

It was the punishment which had been inflicted on traitors of ten generations.

All that was new was the procedure; and, if the new procedure had been intrinsically better than the old procedure, the new procedure might with perfect propriety have been employed.

But the procedure employed in Fenwick's case was the worst possible, and would have been the worst possible if it had been established from time immemorial.