What are the potential risks for both parties in entering into a supplementary agreement?

When work is added to a contract via a supplementary agreement, the first thing to ensure is that the agreement in in accordance with the terms of the original contract. The supplementary agreement is required to specify the extent of any additional work as well as making clear any adjustments that are necessary as a result of adding the work. Should a supplementary agreement ignore these facets then it runs the risk of leaving an architect in an invidious position, with no legal powers and with a client expecting work to be carried out in accordance with two contradictory contracts.