The delays are slowly strangling my wife's business
Welcome to the BT Residential Customers forum
If you are a business user, please could you post on the BT Business forum at http://business.forums.bt.com/
BT do not permit you to use a residential account to run a business, as its against their T&Cs.
BT can try and control the use of residential lines but in practice they cannot effectively enforce those t and cs
It depends on whether you want to be able to claim for actual financial loss, if you have a protracted fault. This is only possible on BT Business. A better SLA is also available.