Why is Scotland so good at electrification when England is so poor?
Although it doesn't feel like it, the Scots actually built up gradually. First was Airdrie-Bathgate, a relatively simple scheme with the big advantage that most of the work didn't involve live railway. This has then moved on picking up a few useful infills on the way, to EGIP which is more ambitious but still relatively modest - comparable in size to the Lancashire Triangle. If Transport Scotland has its way then the next step will be the much bigger project of getting to Aberdeen.
Compare with the English situation. In a period of two or three years we went from having done virtually no electrification for 10 years to committing to three schemes each of which is significantly bigger than EGIP. Two of these are now firmly on the back burner.
I'd say another benefit in Scotland is political concensus - changes of government cancelled EARL and GARL but didn't harm the progress of electrifying the main lines. And from what I see of Transport Scotland, they have a small but highly skilled team of experts who really understand how the railway works and how it could and should be developed.
On a side note Network Rail Scotland seems to have got the point where it is electrifying the right amount of track it can mange and is not biting off more than it chew, so how many track km on average is NWR Scotland planning to electrify per year compared to what is/was planned in England?
They always quote 100 stkm a year as being the ongoing investment.
That's 32-ish miles of double track, and very manageable (much like the NW scheme in fact).
I think there are three things in Network Rail Scotland's favour.
Firstly, as you say is that the programme has developed gradually. Lessons were learnt and engineers were trained on the Airdrie - Bathgate scheme which had the advantage of operating mainly (although not completely) on a closed alignment. A lot of the EGIP management, contractors and engineers cut their teeth on A2B.
Secondly is the relatively sensible volumes / timescales. No one (either Scottish Government or Network Rail) is promising to electrify the whole network by next week, so no one is needing to make promises that can't be delivered and lead to a loss of confidence in both sides as has happened in England.
Thirdly and most importantly in my opinion is the long term vision for the Scottish Network. Everyone in Scotland is very clear about the long term plan thanks to the Strategic Transport Projects Review process from 2008. The STPR set out exactly which lines were to be electrified, in which order of priority, for the next 15-20 years. This means other schemes in these areas can be planned to take account of future electrification, and Network Rail planning for each Control Period has been able to know roughly which areas will be up for electrification next.
For example structure clearance work is already under way on the Shotts line, even though wiring is not due to be complete until December 2019. Equally I'm sure Network Rail Scotland will currently be working up the designs and work requirements for the East Kilbride, Barrhead and Kilmarnock electrification even though they are likely to be CP6 projects, because they know that the STPR listed these lines as the next phase to be tackled.
In contrast the Network Rail RUS Working Group 6 - Electrification Refresh is nearly 3 years on from it's establishment in September 2012 and has yet to identify the strategic ordering of schemes in England & Wales. Project Managers down south don't know whether to specify other schemes for passive electrification compliance whereas in Scotland even areas such as the Highland Main Line, which are at the back of the queue for electrification, are at least in the queue. Therefore schemes like the potential line speed improvements there should take account of future electrification requirements.
There are still a few lines like South Sub, City Union, Maryhill, Kilmarnock - Barassie, Aberdeen - Inverurie that are slightly unclear exactly where they fit into the hierarchy of schemes but the vast majority of lines in Scotland we know exactly when they will be electrified and Network Rail can therefore plan well in advance.