Octopus Energy confirmed it deployed field sales teams in the Autumn. It said that until recently the teams had offered customers deals that locked them in for three years which were cheaper than the incoming April price cap. 

A spokesman said that “some small teams” were still “collecting information from non-customers who would like to be contacted once energy prices stabilise”.

James Daley, of consumer group Fairer Finance, warned customers that locking into a fixed-price contract could cost them hundreds of pounds more than staying on a price cap-protected deal.

He said: “This is not a good time to be switching. It’s fraught with danger. The deals that these salesmen are offering will be significantly more than what customers are already paying. Locking in today is a bad decision. It’s irresponsible for these firms to be pushing these deals right now.”

Mr Daley said customers should “be on their guard” against sales practices designed to get customers to commit to long periods of time given how quickly wholesale prices are changing. “People should ignore cold calls or doorstep salesmen,” he added. 

The cost of fixed-rate tariffs shot up to record highs this month after the war in Ukraine sparked fears over the supply of both gas and oil. The UK and US governments announced a ban on Russian energy imports leading to firms pushing up the cost of the average fixed price deal by more than £200 in a day to £3,400.

There is no limit to what suppliers can charge on their long-term deals. However, customers on default or standard variable tariffs are protected by the price cap. The cap is updated every six months by the energy regulator, Ofgem, and is predicted to increase to £3,000 in October.

A Scottish Power spokesman said: “We work with face-to-face sales partners to promote our fixed-rate products and pay a fixed level of commission. We’re continuing to offer customers the choice of locking into fixed deals that provide certainty over choosing the price-capped standard tariff, which is predicted to more than double before the end of the year.”

A spokesman for Octopus said: “A few weeks ago we bought a small amount of energy during a dip in the market, enough for 3,000 homes. 

“Rather than bank the profits from this, we decided to offer it as a three year tariff to our customers, and also let a limited number of our field teams promote it to customers as well. They stopped when it ran out and we have no plans to restart.”

Earlier this year supplier So Energy was accused of “pressure calling” customers offering them time-limited fixed term deals that could have left them hundreds of pounds out of pocket.