Understanding of Telco / ISP setup with broadband - Can someone explain the physical setup (UK)

Hi all,

Slightly embarrassed to say that in all my years as a network engineer, I don't understand the physical setup of how 'broadband' is provided to a home user. I understand campus and security technologies but when delving into WAN's or ISP land i'm miffed!

I'll explain my understanding and hopefully someone can expand on this or just outright correct me :)

I will refer to broadband (not fibre) as it's the copper layout and the path to the exchange/ ISP I want to understand.

I'm going to use a block of flats to as a basis to try and understand/explain how I understand it.

So from a customers flat they'll usually have at least a pair of copper cables from a BT socket, which will terminate into a junction box. This will either be a comms room on the premises of the flats or one of those green telephony boxes usually located in the road. I'm assuming this copper pair is usually run no longer than 100m in the same way that UTC runs should not be longer than 100m?

From there the local loop is used which is copper? to the local telephony exchange into some sort of switched housing where it's handed off to an ISP router? if the above is loosely correct, when it comes to the local loop, generally speaking how much bandwidth can it support?

What I don't understand really is how certain ISP's can offer X amount of bandwdith but others can offer an alternative amount when the copper lines remain the same to the exchange? Do they own an amount of cabling or bandwidth for the local loop?

Sorry a lot of daft questions, but any advice or decent resources to understand this would be greatly appreciated.