Sky has already announced that it is bolstering its promotional spend by an extra £13m this year, as it wages war on Virgin Media for pay-TV subscribers.
According to head of media at Ernst and Young, Alan Flitcroft, the cost of staying ahead of the competition could eat into the broadcaster's profit margins.
"Together with initiatives to reduce discounted packages, average revenue per subscriber has exceeded the magic £400 per annum," he said.
"All this is great stuff, but it is no easy ride. Expansion into triple-play means that Sky is battling it out with BT, Orange, Carphone Warehouse and more."
Flitcroft added: "Unbundling BT exchanges costs money and the latest announcement is that digital TV subscribers can opt for the basic Sky Broadband Package for free."
Sky now has 8.492 million customers, but suffered a 13% churn rate - the measure of how many customers left the service.
The results show a 34% year-on-year growth in the take up of Sky+, to 2.167 million, exceeding the 25% penetration target it set itself three years early.
The broadcaster's revenue increased by 10% to £376m, including £41m from residential broadband and £117m from Easynet Enterprise.
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