Is there a minimum number required for the show to go ahead?

For the scheduled public shows - 8pm Fridays and Saturdays from September to June - no.

Rain, hail, sleet or Icelandic volcanic ash, if someone has come out to see the show then they will get that show!

For special bookings - private GhostWalks on evenings when shows are not normally scheduled, we don't have a minimum-audience requirement as such, but the minimum fee for such tours is £60, so normal ticket tarrifs (and discounts) only apply after that minimum charge is covered.