BT has signed up more than 500,000 households to its new BT Sport channels, which will air live Premier League football from next month – although the majority are existing broadband customers adding the new service for free.

The telecoms company added just 23,000 new pay-TV subscribers in the three months to 30 June.

BT revealed in its results for the three months to the end of June on Thursday that more than 500,000 households have now ordered BT Sport, the channels which launch next Thursday, 1 August, and will air content including Premier League football.

The company admitted that this is "mostly" existing customers who have taken the channels for free as part of renewing their BT broadband contracts. The majority are also taking BT Sport via satellite, so do not count as standalone subscribers to the company's pay-TV service.

BT announced in May that it would offer its sports channels free to customers who take its broadband service as a way of driving up subscriber numbers.

The company will be concerned that the rate of growth of new pay-TV subscribers has slumped by almost 43% – it signed up 40,000 subscribers in the previous quarter – despite running a star-studded multimillion-pound ad campaign to entice new customers to its TV service. It spent about £1bn on the rights to 38 Premier League matches each season.

Rival TalkTalk signed up 160,000 customers to its pay-TV service in the three months to the end of June.

TalkTalk, which maintains that its model proves there is no need to pay hundreds of millions of pounds for expensive sports rights to win customers, is already close to half the size of BT, with 390,000 TV customers despite launching just nine months ago.

BT has a total pay-TV subscriber base of 833,000.

"BT Sport has proved popular with our customers," the company said. "We expect the proportion of new customers to increase after we launch the channels on 1 August," the company said. "The channels aren't live yet and the Premiership season doesn't begin until 17 August, so this is a strong start."

Andrew Hogley, a telecoms analyst at Espirito Santo Investment Bank, said that there was no expectation in the market that BT would add a huge number of new TV customers at this stage.

"On TV we weren't expecting any pick up in adds this quarter, should start to ramp from [BT's] second quarter," said Hogley. "The 550,000 pre-orders for sports [channels] looks OK – we will see what happens next week when ESPN goes off air."

BT said that it has spent £40m on BT Sport's "pre-launch costs" in the quarter, which will include setting up its top-end studio facility in the former broadcasting centre in the Olympic Park in east London.

The telecoms giant added 95,000 broadband customers in the quarter; TalkTalk reported on Wednesday that it managed to sign up 22,000.

Overall, BT reported a 1% fall in revenues to £4.44bn in the quarter, with profit before tax falling 16% to £449m.

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