Hardcore Marmite fans take note. Marmite Extra Old rolls out to Tesco and Morrisons this week. Marmite 'XO' (rsp: £3.99) is matured for four times longer than standard Marmite and has a thicker texture and stronger flavour.

Unilever developed it together with the social media group Marmarati, which the manufacturer described as a "quirky, Victorian-style secret society for Marmite eaters".