LN-KGL -
I must strongly disagree with your assertion that folks in NW England avoid Norwegian for "nationalistic" reasons. This is just plain wrong. As you know, overseas carriers do extremely well out of MAN when there is strong awareness of their product offering and demand for the destinations offered. Look no further than the MEB3 for evidence of this. And within Europe, frequency increases by carriers such as THY Turkish and TAP Portugal also demonstrate the market's willingness to fly with overseas carriers. Are you suggesting that NW England customers are biased against Norwegians in particular but are fine with Arabs, Turks and Portuguese? This reasoning makes no sense in reality.
Norwegian's challenges ex-MAN lie elsewhere. Specifically, Scandinavia is served ex-MAN by SAS, "British Airways" [to the consumer, Sun-Air to us!], EasyJet and Ryanair as well as Norwegian. I put it to you that all four of these brands are significantly better known in NW England than DY. Most people here are familiar with SAS; BA, Ryanair and EasyJet enjoy very strong market recognition. Norwegian Air Shuttle … not so much. The problem for DY is not prejudice against their nationality, it is market awareness of their existence and of what they do.
The other factor influencing DY's penetration at MAN is that they serve only routes to Scandinavia itself. Beautiful destinations, yes, but also extremely expensive ones for those who count their savings in GBP. Also, Scandinavian cities are cultural destinations ideal for upmarket city breaks, but they will not appeal to the large 'sunseeker' market.
If Norwegian does eventually elect to venture into the MAN - Mediterranean market, they will find zero resistance based on nationality or provincialism. They will, however, have to create brand-awareness to differentiate themselves from widely-recognised strong incumbent carriers such as EZY, RYR, MON, EXS, TOM, TCX and all the rest.
Norwegian Air Shuttle does offer a great product in the cabin. But few folks in NW England know that. And only those traveling to Scandinavia need take an interest anyway. That is nothing to do with conservatism or nationalism. It is about product-awareness … nothing more.