Nalsur,
The contractor is responsible.
The ITP is prepared by the Contractor and this is basically telling the Owner/Client what your intentions are regarding inspection & testing.
The Owner/Client then reviews before the ITP is approved so they can add their Hold / Witness points if required.
If you let the Owner/Client write the ITP you may be up for 100% volumetric examination when the contract was budgeted on 5% ?
Cheers,
Shane