National statistics on average net weekly household income are set out in the annual "Households Below Average Income" publication. Average incomes are not available at constituency level in this publication because the survey sample sizes are too small to support the production of robust estimates at this geography. However figures at a regional level are available as a three year rolling average. National figures are available for individual years.
Figures on average incomes for London and for England can be found in the link below, in table 2.5ts, and sets out median and mean incomes before housing costs (BHC) and after housing costs (AHC). Figures for the UK can be found in table 2.1ts, which shows UK income deciles but also the median and mean incomes, both before and after housing costs.