You will not likely need planning permission for most lean-to conservatories. Historically, building regulations stipulated that a percentage of your roof had to be transparent to be exempt, but times have changed. With a lean-to conservatory in Yorkshire, if you plan to build a structure up to 8m long on a detached house or 6m long on a terraced or semi-detached one, you will not need planning permission.
However, you will need to apply if you plan to put in a roof higher than 4m or install taller feature windows or balconies that rise above your existing roof.
Also, you will need planning permission if your property is listed or in a conversation area.