With regards to inspection of the site, what is the duty of the architect?

This is something of a legal minefield, but can be reasonably summed up thus. The RIBA Agreements necessitate the architect visiting the construction Works for the following purposes:

(a) General inspection of the progress of work.

(b) General inspection of the quality of work.

© Approving elements for which the architect’s seal of approval is required.

(d) Obtaining information necessary for the issue of notices, certificates and instructions.

These inspections should be carried out at intervals such as are reasonably considered to be necessary. Should the architect be able to explicitly display to a court that their conduct has been consistent with the points above then it is highly likely that a court will find them to have satisfactorily carried out his / her duties.