no i think you are the one who is confused:

Y means Economy
Y+ means Economy +
J means business class
F means First Class

I have mentioned that all the prices quoted are the cheapest available in those cabins.

If you want to get into Fare basis then the cheapest are usually:

M (representing the Economy cabin) is £350
T (for WT+) is £650
I (for J) is £1600
A (for F) is £3500