Allocated seating will be introduced on all easyJet flights from tomorrow.
The low-cost airline announced plans to offer the service earlier this year, following a trial period.
It was launched on flights from Gatwick South, Luton, Stansted, Southend, Bristol and Glasgow on November 13, and on flights from Gatwick North, Milan, Rome and Paris Charles De Gaulle last week.
From tomorrow it will be available on all other routes.
The move means that passengers are able to choose a seat when they book – previously the airline operated a first-come, first-served policy.
Under the new system all passengers are allocated a seat number, while those wishing to choose their seat are able to do so for an extra £3. For an additional £12 passengers can reserve seats with extra legroom in the front and or exit rows, and for an extra £8 they can have a seat in the first few rows, meaning they can usually exit the aircraft more quickly.
Easyjet offered allocated seating on selected flights from Luton last summer, and claimed that nearly three quarters of passengers on trial routes were in favour of it.
A survey of 7,400 readers by Telegraph Travel revealed that 95 per cent prefer allocated seating, although only 35 per cent said they would pay for the service.
Paul Simmons, easyjet’s UK director, said: “This is the single, biggest change the airline has undertaken in its history. Our customers told us allocated seating was important to them and the extensive trial has delivered positive feedback across Europe.
“Allocated seating provides a better boarding experience and gives passengers the added choice of selecting a seat for those who want to.”
A number of other airlines, including Ryanair and British Airways, already charge fliers to choose their seats. Ryanair was investigated by the Irish Aviation Authority earlier this year for charging passengers £10 to sit in the emergency exit seats. A number of flights took off with the seats vacant, because no-one on board was willing to pay the fee.