British online grocer Ocado said the huge blaze which destroyed its flagship distribution centre in Andover in England was caused by an electrical fault in a battery that prompted a robot to catch fire. 

Ocado said an electrical fault at one of the battery charging units at the edge of the ambient storage grid caused the plastic lid on the top of a grocery-carrying robot to catch alight. 

The firm said it has undertaken several remedial actions intended to eliminate the risk of such an event occurring again. 

These include the introduction of additional localised smoke detectors and the removal of the plastic lid on its robots. 

Ocado also intends to add heat sensors in the ambient product storage grid which are in addition to the existing sensors in the chilled storage grid.

The details were included in a circular to shareholders Ocado published in relation to its joint venture deal with Marks & Spencer.