@rustybob
TBH, no ISP is immune from exchange or network congestion and adding in more capacity isn't as simple as flicking a switch which can be done overnight. It can take many weeks/months for an ISP to add more backhaul capacity, however there are some ISPs which are pro-active and increase capacity in advance such as AAISP and TalkTalk Business.
I'm with the latter (direct TTB customer) and even though i signed up to an eye watering 24 month contract on their 80/20 vdsl service, they have made it very clear to me that if they cannot resolve any line/broadband fault within 28 days of first reporting it, I can leave them penalty-free d/t some Ofcom business broadband ruling.
TTB's network status page is very detailed, shows what network improvements they have planned:
https://managed.mytalktalkbusiness.co.uk/network-status/