The “big six” provider said 4.76 million of its 6.76 million UK domestic customer accounts could be affected by a cap on standard variable tariffs (SVTs).
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Perth-based SSE joined rivals in raising fears over the Tory election campaign promise, saying it posed a risk for the company and other suppliers.
It said: “SSE would caution against potential unintended consequences of any proposed intervention in what is a rapidly changing and increasingly competitive market.”
• READ MORE: ScottishPower says bill cap could harm competition
The comments came as the group posted full-year figures showing a rise in profit margins at its UK household supply arm despite shedding 210,000 household and business customer accounts.
SSE, which raised dual fuel prices by 6.9 per cent in March, said UK and Ireland customer accounts fell from 8.21 million to 8 million in the year to the end of March as it faced competition from smaller rivals, but insisted it was beginning to halt the exodus.
It said: “While any loss of customers is disappointing, this represents the smallest decline in SSE’s customer numbers since 2013, due to the impact of efforts to improve retention and attract more new customers to SSE.”
Profit margin per dual fuel household customer – a key measure in the industry – was about 6.9 per cent, up from 6.2 per cent the previous year.
This helped lead to a “small overall” rise in annual underlying earnings at its household supply arm, although it said adjusted operating profits fell 2 per cent overall in the energy supply division, to £389.5 million.