An advert for a contraceptive app used by over 100,000 UK women has been banned by watchdogs after figures show it is less effective then suggested.

Natural Cycles is the world's first certified smartphone-based contraceptive which has found itself at the centre of recent controversy as a string of women using the "highly accurate" app have reported becoming pregnant.

The smartphone app, which uses a thermometer to track the user's fertility, has been certified and marketed as a contraceptive since February 2017.

The app's algorithm takes into account factors such as ovulation day, cycle length and the average temperatures of different phases throughout the menstrual cycle. It then assigns a number of green days to notify the user of non-fertile days, and red days - when the user is predicted to be fertile.