For this post we consider households with more income than 90% of households in the UK. Perhaps not all "rich", but certainly "richer than most".
We use the Household Disposable Income data from the Office for National Statistics (ONS).
These ONS figures for 2013 show the top decile (top 10%) of households had 13.4 times more disposable income than the bottom decile of UK households.
[Disposable Income = income after receiving state benefits and paying direct taxes (e.g. income tax is taken out, but not VAT which is an indirect tax). Disposable Income is effectively a household's "spending money".]