According to the Beauvais Airport site, http://www.aeroportbeauvais.com/airport/index_eng.html the bus takes an hour to Port Maillot (Métro line 1) http://offnature.roshd.ir/metro/eu/par/paris.htm

Here is the Prestwick Airport web site http://www.gpia.co.uk/ Use the Quick Links at the top.

Cheers, Linda