Afraid I don't own a PS4. Only just got round to getting a PS3 actually....
I would add to MrNelster's sentiment that you'd find better info/more intelligent and more informed answers elsewhere really. Personally I'd google
your question. It would help to know which app you were using and if all of them encounter frequent buffering issues?
Also - note time of day. If you can download okay from other sites then it's unlikely there's a line fault but you'd need to rule out contention/traffic management - ie, deliberate throttling of certain services activated at particular times of the day for your ISP to manage their traffic. But it sounds more like an issue with the PS4 and that particular app you're using that didn't name that's the issue so I'd include that in a google search and try to narrow it down to UK hits to see if others are experiencing the same issue (which is highly likely).
If it's technical issue then other users can help you set up your router say or talk to BT if it does indeed turn out to be a line issue.