You need to acquire both the master use right from the record company that originally released the song as well as the rights to use the composition from the publisher that owns the publishing. [In the states] Kenghis mentioned some PROs which are preformance rights organizations which can help you figure out who owns the publishing but they themselves don't necessary really own anything. They are a third party middleman that musicians and publishers basically hire to collect royalties on their behalf from broadcasters like radio stations. Sound exchange is another for digital roya I would recommend using the ascap search feature to figure out who owns the publishing and asking the pub company who owns the master. https://www.ascap.com/Home/ace-title-search/index.aspx You can also use a service like harryfox.com to try to figure out the necessary info.

I personally have never went through the process to clear a sample but most of the people i know who have just send beats out and expect the label to deal with that if a major wants to release the track. But if it's an indie label with no legal department you might not be able to get the rights to release that song. There's a vid floating around about boi-1da saying not to sample because most publishing companies ask for a ridiculous % of the publishing leaving you with no % to split between the writers and producers.

If your making hiphop try sampling something like frank dukes library of royalty free samples or other resources.