Router Readings Drop

Does an interruption of service from one's ISP, if the fault lies with BT such as a Central Pipe problem, will that downgrade one's download speed. I have had Router Readings of 7616 prior to the outage and next day readings are 3712 all day since the the failure.

Reboot your router. If it re-syncs at a lower speed due to noise, or a line problem, it may hold onto that lower sync, until you manually reboot. Routers don't normally respond to increases in noise margin (which would allow a higher speed).
If the line problem has gone, once you reboot the router it should sync at a higher speed, although it'll take three full days before your download speed increases.

Rebooted as advised, left off for thirty minutes. Router has returned to 7616 from the previous 3712 as per post.
Note remarks, re three day period before download may increase.
Thanks much obliged.

Spoke too soon. Day later my Router shows the previous 3712, down from the 7616 after a reconnect at 9.30pm last night. The computer was then switched off overnight but the Router was left on.
Today, tried another, disconnect and reconnect, but there was no change from the 3712. Puzzled.