B757
The maximum config on a B757 is 235 seats (design limit).
Jet2 B757s have 229 I believe.
Therefore they are adding 1 (one) row of 6 abreast. to bring the total to 235.
Extra leg room seats around the Emergency Exits (Doors 1,2 and 3) are obligatory to allow for rapid exit in an emergency.
I don't ever remember Thomson or Thomas Cook selling these Emergency exit extra leg room seats on their 757s with a higher APD charge (but I stand to be corrected).