Cheap energy

You could save on electricity and gas costs when the annual contract renewal offer comes.

Ofgem has a list of accredited price comparison sites.  However many don't list all offers, or state them in a tricky way.  My impression is this is the best: energy comparison

The lowest electricity rates that I found for my Saver 7 electricty system in Feb 2018 were offered by Economy Seven and by OneSelect.
This is the OneSelect rate:
Day: 13.6p per Kw
Night: 7.33p per Kw
Daily fee: 24.52p

If you've already received a fresh offer from your existing supplier, you can initiate the process of switching without penalty. 

Nice to hear of anyone getting a lower offer!