Thanks for the advise!
I've tried drain cleaner, no joy. I got a pipe cleaner from B&Q, its like a spring type thing which can go around bends, its approx 15foot long. I put this down the toilet and couldnt feel any blockage.
The soil pipe in internal by the way...
The only thing I did notice which I'm not sure is correct was that where the soil pipe comes out of the wall and into the drain, I noticed a smaller 2 inch white pipe in the middle. I'm sorry I'm not more descriptive but I'm not very good at this kinda thing. Should the smaller white pipe be there?