Just looked at the BT line checker and BT Infinity has moved from 31st December 2012 to 31st March 2013. I live in Hanworth and currently receive ~4Mbps.
Really not happy
As has been said in numerous other threads over the last 48 hours, the end quarter dates are just holding dates indicating BT Openreach's likely prediction for Ready for Service.
Many of these dates are met some time before the end of the quarter. However, some are not and are pushed back - in the case of my exchange, numerous times, the last being for six months. The exchange quietly went Ready for Service six weeks before the end of the most recent 'end of quarter' date.
If work is underway, BT Openreach may well deliver service before the end of March. The changed date merely reflects the reality that it is unlikely to be possible to commission any more cabinets before the end of the year.
Even if your exchange went RFS now, you'd be unlikely to get an install date much before the middle of January.