Most standard forms of building contract provide for written instruction by the Architect/Engineer/SO prior to ordering any variation works.The Contractor is obliged to carry out any variation works instructed (incl. those deemed variations such as statutory compliance), unless its validity is in question.
The appointed QS (if any) is then responsible for valuation of variations under the relevant clauses of the contract. Quotations or price agreement are usually not a precondition under most standard form contract prior to carrying out the variation works.
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