With regards to the radiator, any secured fixings are the property of the employer, not contractor or sub-contractor. If a sub-contractor removes them, they have committed theft.
With regards to the piping, Clause 2.24 states that site materials must not be removed without architect’s consent. However, despite this clause, the sub-contractor may still have a legitimate legal claim to such unfixed materials. The best course of action for the employer is to attempt to secure the site and all materials as quickly as possible in the event of insolvency