It is an unlikely line-up. One minute you are listening to Lily Allen’s latest track, then Eric Pickles interrupts with a message about rising debt levels, quickly followed by the music of Dizzee Rascal.

But that’s what millions will hear when they tune into Spotify, the digital music service, after the Conservatives began advertising on it yesterday.

In a 45-second message between songs the Tory chairman attacks the Prime Minister’s “reckless spending” in an unprecedented attempt to reach the digital generation. “With Spotify, you only listen to the stuff you want to hear, right?” says Mr Pickles. “Well, sorry to spoil your day, but here’s something you don’t want to hear.”

That something is the Tories’ claim that “this country’s debt will double to £1.4 trillion within five years . . . Unbelievably, that’ll be almost £23,000 for every person in the UK”.

Mr Pickles adds: “So sorry for interrupting your listening to tell you all this but we think it’s something you need to hear. And now we’ll let you get back to your music.”

Advertising on a digital music service is a first for a major British political party. It is thought that by using Spotify, the party might be able to skirt some of the rules on political advertising that apply to established media forms. Apart from party political broadcasts before a general election, parties cannot advertise on radio or television.

The Tories hope that their message will reach first-time voters and those aged 30 or under. Spotify’s ability to target listeners by postcode means that the party may look into using it as a means of delivering local messages to voters as the election draws closer.

Mr Pickles told The Times: “I hope this ad will reach and engage with people who normally aren’t interested in politics. It’s vital we re-energise and re-engage people and show them they can make a difference.”

Spotify is one of Britain’s most popular music-streaming services, allowing its two million users free access to tracks in return for listening to short advertisements between songs.

Young listeners said that enduring the adverts was a small price to pay to ensure Spotify’s survival. “It’s a mildly encouraging sign that there are now political ads on Spotify,” said Jonny Ensall, 24, editor of the arts and entertainment magazine The List.

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