Paul Schofield is currently on holiday, however, he had a member of his team, Alex Sanderson, look into this question for you. Here is Alex's response:
All of the big providers have special schemes for elderly customers or those with special needs. These are based around joining a register, which will give the customer access to things like specialist energy efficiency advice, free adaptors for appliances, nominated account handlers etc. They are pretty much the same, but you can contact each one for specific details.
The only one of the main players who offers a specific tariff is Powergen. They have two products. One is an alliance with Age Concern, and is available to over 60's. This is more like the other offerings in that prices are the same but extras offered.
They also have a product called Stay warm, which is special tariff.
Hope this helps, if you need any more detail please let me know.