The National Centre for Excellence in the Teaching of Maths (NCETM) has a self-evaluation tool to help teachers audit their subject knowledge in all areas of the national curriculum, across all age groups. This tool is really useful in identifying where the gaps are in your maths understanding and where to go to plug these gaps. The site requires free registration.
To get to the resource, choose:
Resources > Microsites > The National Curriculum for Mathematics
and then click on a year group and topic that you want to test your knowledge on.