Manipulative robots are spreading fake news online that could be exacerbating volatility in financial markets.

A major study of tens of millions of tweets over two years found that the sheer volume sent by “bots” helped to drive shares in FTSE 100 companies up or down for short periods, effectively moving markets.

Tweets sent by humans typically had a positive impact on stock prices while those sent by robots were more often negative, according to research presented to the Royal Economic Society by economists Oleksandr Talavera, Rui Fan and Vu Tran.

Robot messages typically had an effect for up to half an hour, pulling down prices and increasing volatility.