OT BT home network oddities

[Grizzly]

Hi all (mainly UK BT users)

When I take my netbook to a friends and update/upgrade Ubuntu (sudo apt update 
or sudo apt dist-upgrade) his whole network slows to a crawl, AFAICT my speed 
seems fine (at least compared to my home speed of 5-600k)

The netbook was at one time owned by my friend and he recalls no problems then

his network usually runs at 30-35mb with a latency of 15-20, I can't give an 
actual speed for when I am updating as his network latency goes beyond 500 and 
nothing else works (his smart TV buffers until it times out, the smart energy 
monitor shuts down, his Echo goes to "sleep")

Does anyone know what may be going on?

if it is relevant when update is complete most devices, of which there are 
about 16 (above mentioned plus, Games consoles, a Ruko box, Raspberry Pie, 
tablet, phone, printer, smart light bulbs, BT / Sky box, & an Apple Airbook)