Here is another plant that has just introduced itself into our garden, without any help from me.
As it says here:
Hart's-tongue Fern is a medium-sized fern that can be found growing in damp, shady gorges and banks in woodlands, as well as on rocks, walls and mossy branches.
Which means that the gap at the side of our conservatory must be just like a damp, shady gorge! :)
Ferns actually grow so well in our garden, that they're almost like weeds, but I shall encourage these to multiply in the hope they will shade out the less attractive weeds.