I am intending to purchase two SVR returns from St Albans to Gatwick. Outbound travel will be evening time both ways but on separate days, but one person will be breaking the outbound journey at Blackfriars to travel to another Zone 1 station and back for a few hours using contactless for that excursion. Can anybody please confirm that BoJ is is not likely to be challenged on exit and on re-entry at Blackfriars? As far as I can tell it is permissible but gateline staff may have different interpretations of restrictions (visible or imaginary).