What is the legal position if a contractor argues during work that a tender is too low and that the quality of work delivered should reflect this low price?

[JCT_Experts]

In practice, although individual circumstances and provisions may be taken into consideration in legal proceedings, a reasonable rule of thumb is to state that an employer is legally entitled to receive what has been stipulated by the contract. A contractor attempting to explain away poor work with such arguments as implied by the question is unlikely to find legal support.