Ano Ltd is a publisher specialising in producing scientific textbooks. In January 2013, it decided to produce a new edition of a particular book and commissioned Box and Cox to produce the work. Box was to provide the text and Cox was to produce the extensive diagrams and each of them was to be paid £5,000. The contract entered into between Ano Ltd and Box required the text to be produced by 30 April 2013 and the terms of Cox’s contract required the diagrams to be submitted by 30 June 2013. In March 2013, Box informed Ano Ltd that he would not supply the finished text on time unless Ano Ltd increased his payment by £1,000. Ano Ltd agreed to the increase but when Box submitted his invoice on delivering the text, Ano Ltd refused to pay the additional amount. In May 2013, Cox informed Ano Ltd that he was no longer willing to produce the diagrams for the book. Ano Ltd can get someone else to produce the diagrams, but given the time lost, they will have to pay an additional £500 to produce the diagrams on time for printing the textbook as originally planned.

Required: In the context of the law of contract, advise:

(a) What action Box can take against Ano Ltd to enforce the additional payment;

(b) What action Ano Ltd can take against Cox for his refusal to produce the diagrams.