More people in a home means higher food and energy bills, costing a host around £107 a month more per family lodger, despite around half of those who do move in paying nothing towards rent, the same report suggests. But after tax, the average monthly income for a family in London is £2,344, down by £133 since August 2011, so it’s hardly a surprise that one in five have had arguments over cash. An upfront conversation about how much family members should contribute before they arrive could nip it in the bud.