I suspect that the type of people who make up the audience for a Martin Lewis show are largely the same type of people that subscribe to 'Which?' magazine. They tend to be relatively well off (and, obviously, wanting to stay that way), rather than those who are extremely hard up.
So, for example, most of the people in the audience will be in work (in steady jobs with, at least, 'reasonable' rates of pay) and car owners. There won't be many people in the audience who're unemployed or who are on minimum wage zero-hours contracts and who struggle to find the bus fare to work). Similarly, there probably won't be many people in the audience who're making use of food banks. Those who're only receiving the basic State Pension (topped up by Pension Credit to around £9.5k p.a. in total) are also likely to be under-represented.
Inevitably, if you've got an audience where most people earn at least £35k p.a. (which is around the national average), and with some possibly earning a great deal more than that, there will relatively few of them who're in 'fuel poverty' when compared to an audience which is more representative of the population as a whole.