Thank you Moss for your very interesting and courteous reply to my enquiry. I have made a note of the book you mentioned andwill see if I can borrow it from the library.
I am currently reading a little book by someone called Isabel Hill Elder (Forward by the late Lord Brabazon of Tara) entitled 'Celt, Druid an Culdee'. Although, it is of course subjective, the author writes with immense admiration for the pre-Roman Britons and portrays them as a civilised, hospitableand brave people - the envy of the Romans who were known for their cruelty and slavery.
You may find her view of Avebury of interest (to add to the other interesting but speculative theories).
"The great circle and temple known as Avebury ('Ambresbiri, the Holy Annointed Ones') is of special interest as the Westminster Abbey of ancient times, the last resting place of princes, priests and statemen, warriors, poets and musicians. One of the old Druids alluding to Avebury calls it 'The Great Sanctuary of the Dominion'.
(Apologies if you are already familiar with the above book).