Swedish to English Bus/Financial Law: Contract(s)

I know there are a number of suitable translations for this term, but I am wondering which to use in the context of a tender specification document from Stockholms stad. I am not sure 'client' or 'purchaser' sounds appropriate for a large public contract, but I'm not sure if 'contracting authority' or 'contracting party' is appropriate either.

Any ideas?

Some context:

Endast skriftligt kompletterande uppgift lämnad av beställaren under anbudstiden är bindande för både beställaren och anbudsgivare.