You want a router that can hard limit both inbound and outbound traffic. The vast majority can only do outbound ie upload. Your problem is likely too much download data. That cannot really be fixed since only the ISP can limit it. When the path to your house is overloaded the ISP has no way to tell what is important and non important traffic and just drops stuff randomly.
So what some routers try to do is even after they successfully get data they throw it away anyway for the users they want to limit. This in some cases causes the application to slow its rate to reduce the loss. It does work for youtube but some video streaming application just ignore the issue and accept poor data quality and keep steaming the data at the same rate. So even if the PC does not actually get the data the router does which is still eating the bandwidth.
The one I know does this is the asus rt-n66u. Many of asus higher end routers have this type of QoS. Look at the manual so you can see what the configuration looks like. Many other vendors also offer this but i don't know off the top of my head.
The way you would configure this is sorta backwards. You would put your machine in the "high" group. You would leave all the rest in the "low" group. Then you would limit all the users in the high group to say 6m. This would leave you 4m for your machine. You must set the limit for the low group a lot lower than you really need. It will still spike above that so it does not work well to set it too high. Of course the major problem with this design is this limits the other machines even when you are not using the connection with you game machine. The extra bandwidth is wasted.
Hmm so what would you say is the best thing that I can do? is there software that I can put on their machine that could perhaps limit it that I can control remotely? or? what are the best routers that I can buy to be able to help with this, I am not looking for some thing cheap but not something ridiculously expensive. Perhaps around £100 ish?