OK thanks again for these points, next time I get screwed by BT I'll be sure to get these technical details accurate.
I think the problem here is that everything is now done online and it is all computer automated without any human intervention.
I don't know if how it works but I suspect it is something like this:-
The ordering process is through BT ISP which will, because of the automated system, happily take your order because the data base supplied by Openreach that the computer is working off, registers that there is availability at the cabinet. Once the order has been taken it automatically issues an activation date.
After that has been done BT then contact Openreach, probably via a computer request and arrange for the activation to take place. It is only at that point that BT learn if there is either no dates or capacity available and if need be, the customer is advised of the problem with dates or activation.
At no point through out the process will any checks be made for faults on the line or at the exchange, because this all takes time and money and the percentages/risk management probably work out that is more economically viable to fix problems after the customer has signed up than to run those checks before hand.
In my opinion the main problem is that there are two companies involved in providing this service to the customer and they both blame each other for the problems and don't have a customer centred approach.
Openreach who are responsible for the infrastructure and basically have a monopoly so don't have to worry about pleasing their customer,BT and BTISP who do not do enough to keep the customer informed and work for the customer rather than against them. They do not appear to do enough to resolve problems as quickly as possible and with as little hassle to the customer.
They also appear to let Openreach get away with a lack luster approach to supplying their monopolised product without any come back.
BT seem to forget that the onus is solely on them as the company that are contracted to supply a product do do so in a professional and efficient manner.
Thanks gg30340 - I think you've got that absolutely spot on.
To be honest I didn't realise that BT & Openreach are that separate, this was my frustration.
I think more should be done to manage the network infrastructure so people aren't misled - whatever ISP is making the promises.