>>> I've never heard of Jet2.
Jet2 is largely a 'northern' airline, with no services from any of the London airports (or anywhere else in southern England). They flight out of Belfast, Blackpool, East Midlands, Edinburgh, Glasgow, Leeds/Bradford, Manchester and Newcastle. Consequently their advertising tends to be placed in the northern editions of national newspapers (although their ads appear on the London Underground as well), so many southerners might be unfamiliar with Jet2. However, with over 50 aircraft and carrying more than 5 million passengers per year, Jet2 is a major player in the low-cost market.