Can I put some form of ducting through the concreate base of the
conservatory to enable air to still pass through the airbricks,
or do I need to build some form of suspended floor for the
conservatory, and place further airbricks in the outer wall of
the conservatory base ?

Either solution is acceptable.

I used the suspended floor solution, although this was mainly because it
would have been extremely difficult to get sufficient concrete in for a
conventional base, as I have a mid-terraced house with no rear access and
access through the house would have precluded wheelbarrows.

http://www.ezebuilder.co.uk/page3.html

Christian.