I posted the policy last week - they are not allowed.
Helena Bowman from MFC stated at the last fans firum
HB advised that smoking, including the use of e-cigarettes, is banned fully from the Riverside and where possible the club will take action against individuals using vapes. HB advised that the EFL are currently looking into a campaign to highlight that vaping is banned in stadiums and MFC will use various channels including the big screen, programme etc to remind fans that it is banned within our stadium.
HB advised that supporters who witness people using e-cigarettes should report it to a steward. Supporters using vapes will be given words of advice, but the Club reserves the right to take further action if the problem persists.