Received pronunciation resources

Hello Everyone,

I wonder if you could help me. My job requires me to speak using "received pronunciation" a lot of the time. My native accent is a northern one, and although most of the time I can speak RP without many problems, there is sometimes a hint of an accent. Could anyone reccomend any books or online resources which I could use to really "polish" off the usage of RP?

Thanks and Best Regrads

Serge