You absolutely can get Granny smiths all year round in London, or anywhere in the UK.
My personal issue with them is they can be 'waxed' (sprayed with some sort of petroleum product) - but often they don't have this.
My personal issue with them is they can be 'waxed' (sprayed with some sort of petroleum product) - but often they don't have this.
> The materials used to wax produce depend to some extent on regulations in the country of production and/or export. Both natural waxes (carnauba,[12] shellac, beeswax or resin[4]) and petroleum-based waxes (usually proprietary formulae)[3] are used, and often more than one wax is combined to create the desired properties for the fruit or vegetable being treated. Wax may be applied in a volatile petroleum-based solvent but is now more commonly applied via a water-based emulsion.[5] Blended paraffin waxes applied as an oil or paste are often used on vegetables.[7]
https://www.wikipedia.org/wiki/Fruit_waxing
Btw, shellac would make the apple non-vegan as it is made from insects.
Basically, the wax is a non-issue if you skin them.