I have moved to Octopus's Gas Tracker tariff which follows wholesale prices and changes daily. So far so good. Today gas is 6.64p/kWh, compared to just over 10p/kWh on the regular tariff.
For the rates during January, http://mysmartenergy.uk/Tracker/West-Midlands#TrackerGas
You can flip back to the old tariff if prices go crazy again.