Wally, you'll need to find out who owns the publishing to the track and approach them. It's the publisher, not the artist or even the record label that owns the rights to the sample clearance. Sometimes, and I mean very rarely you can approach the artist and their management directly if they're sound (I had this very lucky instance with Banco de Gaia and 808 State) and you can sort it through them, but generally you're left dealing with an entity who owns the publishing rights. Most artists (sadly) don't own their publishing.
In order to find out who owns the publishing, dig out the original track and look at the credits. It will say 'published by ___'. I'd recommend getting an entertainment lawyer on your side, or at the very least someone who's very familiar with negotiating licensing deals. I can refer you to someone to speak with in the UK who'd be able to assist if you wish. Drop me a PM if that's the case.
If it's a major label like say, Universal, you're likely fucked. You won't likely get clearance and they probably won't return your inquiry.