Dealing directly with an energy company might seem like a fail-safe way to get the best price from it - but it's not necessarily the case. The cheapest deal for half of the biggest energy companies was not available directly from their own websites, according to our snapshot investigation.
We checked the websites of 12 of the biggest energy companies in December 2019 and compared the price of the cheapest deal quoted to us with the cheapest deal available elsewhere from the same company, according to available whole-of-market data.
A customer using a large amount of energy in the east of England, for example, could have ended up paying nearly £300 more per year by picking a tariff from one supplier's website than they would have paid had they looked on a third-party comparison site.
Read on to find which suppliers didn't list their cheapest deals on their website in our investigation and how to get the best deal from your energy company.
EDF Energy, Eon, Npower, Octopus Energy, Scottish Power and SSE all had cheaper tariffs available elsewhere than those listed on their website, when we checked for three homes using different amounts of energy in different parts of Great Britain.
A household in the east of England using a large amount of gas and electricity would have paid £296 more per year by picking the cheapest deal offered on EDF Energy's website, compared with the cheapest EDF deal sold elsewhere.
Homes with medium energy use in the south of Wales and low energy use in north-west England would also have paid more with EDF Energy than with other suppliers in our snapshot investigation - by £193 and £138 per year respectively.
The chart below shows the big companies whose cheapest deals weren't available on their website when we checked, and the price difference between the lowest-cost deal we found on their website and elsewhere.
Scottish Power's cheapest deal on its website was £200 pricier for our high user than its cheapest deal available elsewhere. Our medium user would have been worse off with Eon - paying £123 more per year with the cheapest deal on its website versus the cheapest deal available elsewhere. Similarly, our low user would have missed out on £116 of savings per year not checking beyond Eon's website.
The other six companies we checked had their cheapest price available on their own websites. These were Avro Energy, British Gas, Bulb, Ovo Energy, Shell Energy and Utility Warehouse.
The cheaper deals we found were often available via price comparison websites. They're often 'exclusive' deals with one specific site - so you have to go to it to sign up to the deal.
For example, both Eon and Npower's cheapest deals had 'exclusive' in the name, while Octopus Energy's cheapest deal was called uSwitch Octopus 12M Fixed.
Almost a sixth of energy customers have been with their supplier for more than a decade, according to our survey of thousands of customers last year.*
Even if you're happy with your provider's service, it's important to double-check prices before signing up for another year or two.
Your energy company has to tell you whether or not you are on the cheapest tariff for your preferences and circumstances - often this is on your bill in a section titled 'could you pay less?'. This is according to rules from the energy regulator Ofgem.
But this doesn't have to include tariffs only available via third parties, such as price comparison websites. Ofgem told us that often these tariffs are often available only to new customers.
If you're happy with your current supplier's service then it's worth checking that you're happy with the price too. Use a price comparison website (and select the whole of market view) to make sure.
We got quotes from 12 of the biggest energy suppliers in Great Britain for a high user in the east of England, medium user in south Wales and low user in north-west England in December 2019.
Usage is according to Ofgem averages for high (4,600kWh electricity and 17,000kWh gas), medium (3,100 kWh electricity and 12,000kWh gas) and low (1,900kWh electricity and 8,000kWh gas) users per year. Deals are based on paying by direct debit with paperless bills.
Whole of available market data is from Energylinx.
*Online survey of 8,353 UK energy customers in September 2019.