Number Sense: Foundation ( Intermediate):
Rounding & Estimating, Negative Numbers, Ratio & Proportion, Multiplication and Division:  http://www.bbc.co.uk/schools/gcsebitesize/maths/number/roundestimaterev1.shtml

Number Sense: (Intermediate & Higher):
Numbers; Fractions, Decimals, Percents and Ratios;  Factors, Powers and Roots: http://www.bbc.co.uk/schools/gcsebitesize/maths/number/

Prime Numbers, Factors & Multiples:
Factors and Multiples: http://www.bbc.co.uk/schools/gcsebitesize/maths/number/factorsmultiplesrev1.shtml
Prime Factors: http://www.bbc.co.uk/schools/gcsebitesize/maths/number/primefactorsrev1.shtml
Highest Common Factor and Lowest Common Multiple:
http://www.bbc.co.uk/schools/gcsebitesize/maths/number/primefactorshirev1.shtml