At least one of the Derby E400's has now arrived, as it can be seen tucked away at the back of the depot, near the rear workshops. The batch are believed to be:

4400 - YY 14 LHD
4401 - YY 14 LHE
4402 - YY 14 LHF
4403 - YY 14 LHG
4404 - YY 14 LHH
4405 - YY 14 LHJ
4406 - YY 14 LHK

This ties in with an earlier post about a YY 14 registered bus having been seen around J28 of the M1.