Are all of the GN 700 services supposed to be 379s when they all come in?
No. Since May 18 there’s always been around 8x 700/0 diagrams on the GN side, not including Sevenoaks. More recently there’s also been 1x 700/1 diagram (which does a peak Peterborough) nominally off the back of Littlehampton ending.
Whilst there’s a little bit of slack in the 379 and especially the 387 diagrams, this isn’t enough to eliminate 700 working, and we’re still at a point where the full 379 fleet isn’t available yet, though there’s still a small handful of additional 387s on GN above the planned 13 units.
It would be possible to reduce the 700 operation a bit if desired, and I’m sure the slack in the 387 fleet has been left deliberately to allow them to cover 379s and 700s.
The obvious next uplift on GN, if required, would be lengthening one or more peak Peterboroughs to 12 cars, so that would account for a couple more potential Electrostar diagrams in the future.
One change this month which no doubt will be a positive for some has been the elimination of normal 700 use north of Cambridge. Given how the 700s seem to have quite often managed to escape to north of Cambridge over the years since their introduction, I wouldn’t be surprised they will re-appear there at some point though, especially during engineering work timetables.