My network crashed hard today and you won't believe why

[DJ-Daz]

It's taken me about 2 hours to narrow down the issue, but my problem was this.

Slow internet (300kb)
I couldn't access my router from Virgin Media, instead it kept taking me to a Sky router instead.
I know Virgin were upgrading this street last week, so I thought maybe they'd crossed some wires, not really possible, but that's what I'd thought after a while.
I initially thought I'd been hacked, and my DHCP raspberry Pi was pointing all my hardware to the Sky router instead.

I did a lot of swapping hardware, and using a spare RPi to see if I could solve the problem, then later to see why it's replicated.
I even turned off every wifi device in the house.
I resorted to scanning the neighbourhood to see if I could find the SSID that the router was using. The house is 50 metres away.
Luckily they were out, otherwise there's a good chance there'd be a right proper slaggin' match.

In the end I found out after disabling everything what the cause is/was.

This morning I'd decided to reconnect my CCTV to the network, but instead of running loads of cable everywhere I used 2 old power-line adapters, and it's these that were talking to the house router 50 metres away!

I
MEAN
WTF?

Try to get them to talk to another device in a different room and you can forget it. But a house 50 metres away... sure no problem!