http://www.tfl.gov.uk/corporate/media/newscentre/25748.aspx

Excerpts...

---quote---
[...]The first batch of 30 buses, enough to convert a full route, will
enter passenger service in April next year [2013].
[...]
No decision has yet been made on which routes will be converted, however
the new buses will be deployed on busy central London routes where their
unique characteristics, such as the open rear platform, can deliver the
maximum benefits."

In a departure from the current bus ownership model, TfL has also taken
the decision to purchase the buses directly from the manufacturer. This
will secure a better unit price by purchasing the new buses in larger
numbers rather than a bus operator ordering in smaller batches on a per
route basis. The buses will then be allocated to the bus operators,
reducing contract costs as the operator will simply quote for staffing,
fuel and maintenance costs.

The new ownership model will enable us to more easily move the buses
between operators when route contracts change and significantly extend
the operational life of the vehicle. After an initial purchase outlay
this ownership model will deliver savings of tens of millions of pounds
over the life of the buses. The TfL Business Plan is due to be revised
later this year and the purchase of the 600 vehicles will be delivered
within TfL's current funding settlement.
---/quote---


Also, in the footnotes to editors - "The operational life of the New Bus
for London is 14 years in service in London."