Brilliant, that explanation certainly makes the I2C bus a lot clearer, I've been wrongly under the assumption that the SDA and SCL lines take their operating power from what ever voltage device they are connected to.
So to clarify SDA and SCL to the RTC (powered by 5V) via 2.7k resistors. Then out the back end of the RTC into the ADLX (powered by 3.3V)
Thank you very much
123Splat, I've downloaded this to my reader, this will be something I'll definitely take the time to read, thank you
Edit
Scratch that, I've just seen how to wire external pull up. I'm now looking into disabling the internal resistors