It's been gone for longer than that - 3/12/11 if this old post on the BTCare forums is accurate.
The way to get a discount from that point was to take Line Rental Saver, for which online billing is mandatory. Unfortunately in my case, BT would only let me have Line Rental Saver on one of the two lines on my account, even though I was happy to pay in advance for both. This makes a second line an expensive option.
If the costs of landline telephony keep rising this fast, I'm going to have to think again about our second line.
One option would be to take the number to a VoIP provider, though the consumer providers no longer seem to offer number porting and the business provider packages I looked at didn't make sense for a single line. In addition, I'd fear losing the number by not being able to return to donor or port it onwards later.
The other option would be to go to a cheaper provider and only take unlimited calls on one line. As my mobile has unlimited calls and doesn't have a 'redial after an hour' requirement, I make a substantial proportion of outgoing calls on my mobile anyway.