Commuters are being warned to expect major disruption across London Undergound as workers prepare to begin a strike expected to last until Friday. Industrial action by RMT members will start on Sunday evening and last until Friday morning. Transport for London says the mass walkout, from January 7 until January 12, will mean ‘little or no service’ across the London Underground network if the prolonged strike goes ahead. Travellers planning to use the tube on Sunday, January 7 are also being warned to complete their journeys by 5.30pm at the latest, in readiness for the walkout while on Friday,…