Advice on breach of contract for building work

We are currently getting building work done that has taken 8 weeks longer than the original 10 week timeframe provided by the builders. 2 weeks ago I issued my builder with a 'Consumer Rights' notice requesting the work complete within two weeks. It was since extended to three weeks. I need advice as to whether I have followed due process and whether I have every right to 'sack' my builder for breach of contract without further charge. I want to give a full breakdown of events for a professional to review, and provide advice accordingly.