According to this Reddit post by reddit user /u/HostileApostle420
” no one in her office is allowed to log into their computers due to ‘mcafee system update’. IT saying people will loose their data if they log in? “
Some of the comments suggest this could be a ransomware attack, especially considering UKPN is one of the largest power providers in the UK
This comes the same day that UKPN announced they are doubling their energy capacity at London City Airport