I've always had a low opinion of the Modernisation Plan diesels - with a few honourable exceptions (Deltics at least), generally either under-powered, overweight or unreliable, and in some cases all three. Sometimes (40 v. A4/A1 or Coronation), not capable of the same peak performances as the steam locomotives they were intended to replace (though to be fair, easier to drive and probably more consistent, but it's interesting to read the disappointment expressed by some experienced performance loggers - I particularly recall Cecil J. Allen being surprised at the first 40 on the GER not being up to a good Britannia).
I've always liked the idea of a BR that electrified more and earlier and kept steam longer on peripheral routes, as happened in, say, Germany (it would have kept me train spotting beyond twelve), with any development of diesels preceded by careful design and testing that might (though probably wouldn't) have given British constructors something that could compete with US product. When
@iainbhx did his railrover tour of a current no-Beeching BR, I started something similar set in the mid 70s in my high-oil price no diesels ATL, but never finished or posted it.