Good afternoon,

Thank you for your answer. 

But due to my location in Scotland: Evri is no option for me,  no Evri where I live.

Can only use Royal Mail + ParcelForce ( = 1 company now )

But it seems some private sellers can add ParcelForce for items longer than 61 cm. 

I have a wicker basket that is 78 cm long and custom postage is not available when I list it. Tried a lot of different categories. Some sellers can add ParcelForce option on category : "Baskets". Not me.