I think dk1 is saying the Norwich Liv St service no longer includes the peak extra that used to sit in Orient Way all day (or go to Bounds Green for servicing as happened for a while)
The basis problem with the 745 arises because the promised timetable re-cast has not been delivered. The order of 10 first class units was on the basis of the below, with Norwich to Liv St in a standard time of max 1hr45mins, so the units would cycle every 4 hours, requiring 8 diagrams. Now the peak Stansted is back up to 4tph (and likely to be increased to all day before too long as loadings are good) there is much less spare capacity in the Stansted 745 fleet. So only way to resource the Norwich is to use 755s. Might as well use them, plenty spare, as the 755 order was to cover extension of some East Suffolk services to Liv St, doubling of Ipswich to Peterborough to hourly, uplift in Yarmouth service, and extension of Norwich to Camb to Stansted all day. None of this has been delivered and not likely to be (other than some Norwich Camb extensions to Stansted), so 755s spare for the forseeable future.
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