It was one of Britain's brightest tech start-ups, praised by David Cameron, and a rare British "unicorn" - a company valued at over $1bn (£694m) before floating on a stock market. Its dynamic founder Dan Wagner claimed last year that his business was worth $2.7bn (£1.9bn) and had signed a deal in China with "limitless" potential. But last month Powa Technologies collapsed into administration - and it rapidly became clear that it was more akin to a lame old donkey than a unicorn. Its demise has raised questions about the health of London's much vaunted fintech (financial technology) sector, and about the wisdom of sky-high valuations for unproven businesses.

http://www.bbc.co.uk/news/technology-35860814