Flexicrew is a form of
'disguised employment' - just like the Ryanair F/Os on Brookfield and Storm McGinley contracts.
It is therefore considered to be illegal under the tax rules set out by HMRC and in particular
IR35.
Google it.
How the conversation should go when BALPA go into see Easyjet management:
"Recruit people on permanent contracts or HMRC/media get a phone call about this company's 'dirty' tax avoiding/evading ways... Tax avoidance. A very hot topic in the media at the minute..." 
"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." - George Bernard Shaw