Not having a written contract is always an error. There have been many cases in which this has been the case, and one could give an extensive answer to this question. The best way of summarising the situation would be to say that every such case is dependent on its own particular circumstances which will be taken into consideration by a court, but that though a contractor may have acted in accordance with what they perceive to be a supposed contract’s terms, the court is unlikely to simply accept this at face value in the absence of further evidence to support this conclusion.