A few days ago, I noticed lots of aphids and ants on a dark red rose bush on our estate in SE1, when sitting on the retaining wall in the sunshine, then looking closer noticed small upright red objects apparently glued onto the topside of the rose leaf, mid-height of rose, with other leaves over them.
These are Lime Nail Galls and are caused by the minute mite Eriophyes tiliae (Acari: Eriophyidae). There is also a clue in the name as the host plant for these galls is Lime and the galls in your images are on Lime leaves and not the rose. Looks like you have a Lime stump hidden in the shrubbery, or this is a sucker from a nearby Lime tree (but then I don’t recall that Lime is particularly prone to suckering). The wiki page seems pretty informative and accurate.