There is a very sound system of control to ensure that under the Financial Administration Act any officer who is receiving goods must certify the goods were received before payment can be processed. This is called certification under section 34.
The things that Public Works buys for itself to maintain buildings or other things are certified by its own officers in that way. The things that are being delivered to other government departments must be certified, with invoices passed to their finance officers to pay. So that is definitely a control there.