On Monday, 3 December 2018 15:47:10 UTC, R D S wrote:
I've 80mb fibre at my workplace, and I get almost full speed.

But it gets slower and slower over the course of several days to the
point of unusability, then I reboot the router and it's flying again.

What would cause this? Stuff beyond my control, or is it possible it's
my gear?

It's not a fancy setup, Technicolor router with a couple of PCs plugged
in and a downwind switch with a PC and a printer plugged into that.
Laptop and mobile connecting wirelessly.

What could cause a network to clag up?

Crap cables can cause problems, I've seen it before and slightly broken or intermitant will cause errors and the error checking increases bandwidth as it resends the data.