Well technically, if you want to talk numbers, there's around 10x the number of people in poverty in the US than there are in the UK, there' was a spike of nearly a million people in the US in poverty last year to around 50M people, whereas the number of people in poverty in the UK is set to rise from just under 6M to 7M by 2014.
Interestingly in the US California has the highest poverty rate as it's one of the toughest states to qualify for state aide, there's also a high racial correlation component in the US, with 25% of African Americans living in poverty
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(Overall rate is 16% of US citizens live in poverty in 2012)
Now what constitutes poverty in either country is interesting, in the UK poverty is normally referred to as "relative poverty" i.e socially defined and dependent on social context, hence relative poverty is a measure of income inequality. Usually, relative poverty is measured as the percentage of population with income less than some fixed proportion of median income. There is very little absolute or extreme poverty in the UK because of advanced social welfare infrastructure, i.e benefits, social housing, NHS etc.
However in the US, there is more widespread extreme poverty with 2011 levels of Extreme poverty (HOUSEHOLDS existing on less than $2 a day) were DOUBLE that of 2006 levels, which means that 1.5M households were said to live in extreme poverty with over 2.6M children affected (this level of poverty is similar to poverty levels seen in the developing world). [Seriously, whole households on $2 a day?!]
in 2013 Child poverty has actually hit a record high in the US, with 16.7M children living in food insecure households.
Interestingly the US defines it's poverty level in 2012 as set at $23,050 (total yearly income) for a family of four, the UK as £18K a year or about $28K However, in the UK, this after housing costs are removed, but that is not true of the US figure.
So basically the US government thinks you are in poverty at quite a low figure, however the UK government considers you to be in poverty a lot sooner (cost of living not adjusted)
But yeah, in the US if your family of 4 survive and pay rent/bills/food/healthcare etc for less than $2000 a month you're in poverty.
If you're in the uk your family of 4 survive and just pay for bills/food for less than $2300 a month, you're in poverty.
So, in conclusion - the US has five times the population of the UK but 10x the amount of people below the poverty line, in addition the US defines the poverty line as lower than the UK does, which would actually push this ration slightly further in favour of the UK having less people in poverty.
Personally I think people see less poverty in the US as it's more economically segregated than in the UK, in London a poor area is less than ten minutes walk from the tower of London, next to 10M houses, in the US ghettos are more prevalent and thus easier to avoid, and entire areas are dependent on certain business which when they fail makes a whole area more economically depressed.
Someone's mentioned Boston here, in Boston you could pay $350K for a duplex, in Detroit you could buy an entire street for that, if not more.