Every evening I seem to have a patch where my speeds go down to around 1500 mbps...What I want to know is that makes the connection suddenly jump from always getting 1500 to always gettin 1800 to 1900?
Its called Contention.
As more and more people start getting faster speeds then the "Sharing" of the network is seeing a greater impact on your connection.
The network is busier in the evenings so you see the effect more.
BT should eventualy apply more capacity to the network to keep pace with the massive growth that is happening at the moment.