Sudden change in broadband speed

[#1]

Hi all,
I've had a recent issue with broadband latency and bandwidth that began at the start of February.
We had the line set up in September 2015, and had no issues with any devices, speed or latency. Recently however when streaming via one of our devices (a phone or roku stick) we have experienced serious speed and latency issues in other applications such as games on laptops, or even internet browsers.
I appreciate streaming is a huge hog on resources, but we have not changed our data usage, and previously had no problem, playing games while also streaming.
All devices are currently used wirelessly, we have tried changing channels, resetting the router and the devices all to no avail.
Any help would be greatly appreciated, thanks.

[#2]

Hi AlexC,
Having taken a closer look the estimate for the downstream on your connection is 6mb and bearing in mind a connection over WiFi will drop that a little further I would expect there to be some issues whilst you're streaming, especially in HD.
Whilst I'm not suggesting this as a solution it could be a good idea for you to run a speed test whilst connected to the router over ethernet. This way we'll get a clearer idea if this is related to the connection itself or is perhaps more related to WiFI.

[#3]

With a wired connection, and having set our roku device to to a max download rate of 1mb/s we are getting latency of between 200-300 ms while streaming. With noticeable delays on even simple internet browsing. Even with a typical downstream of 6mb this should not be case surely?
Edit: We have tried the same thing with a download rate set to 0.3mb/s (a very poor quality stream) and we are still having a latency of 250 ms. Our typical latency with no stream running is 50 ms or lower. Running a secondary application such as a game even at this rate is not possible.
Edit 2: after resetting our router, we're now experiencing wildly fluctuating latency. Via pingtest.net its jumping from anywhere as low as 30 to as high as 300 with the occassional spike reaching 1000, while streaming. jitter is sitting around 100 ms. download speeds are varying between 1 and 6 mb/s (speedtest.net).

[#4]

Further update,
We've done some speed tests and ping tests while no applications are active, and download speeds are still incredibly slow on intermittently, with latency spiking up to 100 ms for no reason.
Unsure of how to proceed.