Builder presenting final bill above estimate for extra works not in estimate

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Hi I would be most grateful to learn if a property management agent who is renovating a property for a landlord/owner and who has estimated for those works can then present a bill that is significantly above the original estimate, without having first made recourse to the landlord/owner as to the additional cost of these extra works i.e. without gaining the landlord/owners consent.that it was ok to carry out these extra works at that additional cost. (There is no question here that the extra works were necessary in order to render the property ready for letting - just whether it is encumbent on the builder to notify the landlord the cost of the extra works and first obtain the consent of the owner before proceeding -  in order to avoid unplanned expenditure at a time when capital is so tight. What recourse could a landlord/owner have in such circumstances please?