Unfortunately I'm going to be no help Jill. We live in the middle of nowhere and have no gas. As our sole energy source our electricity is on a special tarriff which only one supplyer will provide so I haven't been able to get into all the energy comparing myself.
But there are some fairly straightforward site where you can compare tarriffs like this one http://www.uswitch.com/gas-electricity/ppc-rev/dua
or our old favourite MoneySupermarket whihc has a section on it.
I can't do numbers anyway but all this different tariff bit is sooo confusing. You would think that they would just automatically give everyone the cheapest one. But that is probably being very naive.
I hate it when people stop me in the town and start trying to get me to change providers. Not good with strangers in the first place and this throws me into a greater panic.
You could take a look at the Which? website too Jill, there's a gas and electricity section there with some good advice.
In order to get rid of people easily from the doorstep I say I'm a renter! In the street I just say "no thanks" and keep on walking.