BT Vision added just 21,000 new pay-TV customers in the three months to the end of June, as a slump in interest in the service led to the lowest subscriber increase rate in two years.

The telecoms giant's content subscription business, which from next season will be the home to almost half of Premier League's prime matches, grew its pay-TV subscriber base to 728,000 as at the end of June.

BT Vision, which confirmed it will launch a bundled YouView service in the autumn, has not had such a low number of subscribers since it managed just 14,000 sign-ups in the three months to June 2010.

Analysts said BT Vision has been hit by a major shift in rival BSkyB's marketing strategy which focused on advertising its TV services.

"As of April, BSkyB moved all its marketing spend away from broadband to TV, to maximise the launch of the Formula 1 channel and coverage of Euro 2012 and the London Olympics," said Giasone Salati, a media analyst at Espirito Santo Investment Bank. "BT is likely to come back to better TV numbers soon, on the back of the commercial launch of YouView in September."

Last month BT broke Sky's stranglehold on live Premier League football paying £738m in a three-year deal for 38 prime matches a season starting next year.

On Tuesday, rival Virgin Media reported an increase of 37,000 pay-TV customers in the second quarter, taking its total pay-TV subscriber base to 3.7 million.

Parent company BT also reported a slump in broadband sign-ups, with 85,000 new customers in the three months to the end of June.

This is the lowest number that BT has managed to sign up since the end of September 2009, when it managed 71,000 new customers.

BT pointed out that this is 50% of the 170,000 net additions across the market in the second quarter.

"We are very pleased with our BT Vision and broadband numbers," said a spokesman for BT. "The numbers might be lower than those we have seen in recent quarters but the first quarter [of BT's financial year] is traditionally a quiet period and so we are pleased with them. It is very clear that Virgin is stuck in the traffic when it comes to recruiting new customers whilst we are in fast lane."

Virgin Media added 4,000 new broadband customers in the second quarter, compared to a decline in the same period last year, to take its total broadband subscriber base to 4.1 million.

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