The blunder, which affected Feed In Tariff (FIT) scheme members – those who have solar panels fitted – resulted in customers receiving postal mailings meant for other people.

The letters included the customer’s name, address, payment amount and FIT reference number.

But energy giant Npower said that at no point were any bank details disclosed. However, it added that around 5,000 customers received the letters in error.

A spokesperson, said: “We are aware of an issue with a postal mailing for our Feed In Tariff Scheme meaning some customers received letters meant for other people.

“We’re urgently investigating how this occurred with our fulfilment partner (who sent the mailing on our behalf).  We apologise for this error – especially to the customers whose information was incorrectly shared.

“We’ve notified the Information Commissioner’s Office of the incident.”