Once a contract has been practically completed, does the architect have the legal power to give instructions?

There is no legal reason why the architect shouldn’t issue instructions after practical completion, although certain conditions must be satisfied, and there are exceptions. JCT Standard Building Contract 2009 clause 3.10 permits the architect to issue instructions regarding any issue that is explicitly authorised by the contract. However, instructions under some clauses of the contract will not be appropriate once the contract has been practically completed.