I agree that the easyJet private forum is probably a better place to discuss these things.
There is no such thing as paying no tax when on the Spanish contract. You will always pay your tax in Spain. The salaries in a good month are very close to what Flying Clara said. Flying for Air Europa or Iberia you will be on about the same money.
In Italy and France the same applies. The quoted figures are after having paid tax in Italy/France as a resident. Depending on where you choose to live (and commute) then your tax-situation might be more favourable or less favourable. I have heard about even higher takehomes for Paris based guys who commute to a certain EU country with a (still) very favourable double-tax treaty. (I am very happy for them)
I imagine that local pay is benchmarked against the pay of the local airlines instead of benchmarked against the UK contract (well maybe, if the pound was still worth 1.50).
This has got nothing to do with the SXF/DTM tax issue. (been there, done that). When based in Germany we were using a loophole in European tax legislation. Although fully legal we knew this would not last. I accepted this from the very beginning and decided to move when I started to feel the bratwurst-tax breath in my neck. It's just now that the weak GBP is making life more difficult and uncertain for the SXF guys.
If you like the pay, come and join us here. Or try to negotiate the same. I must also add that the current exchange rate makes the local contracts look very good. It's not unlikely that the GBP will pick up.