Concrete removal is tough. The problem is that 99% of soils you encounter will be acidic in nature, as a result the vast majority of cleaning products of cleaning products are alkaline. Cement/concrete is the opposite, it is quite strongly alkaline/basic in nature so normal cleaning products have little effect - you need an acid. Unfortunately, acids tend to be unfriendly to paint work.
Hydrochloric/Muriatic acid is often known as brick cleaner and is a cheap and extremely effective way of removing stains like this. However, this is one nasty acid and I would never consider it safe for use on paint.
Phosphoric acid is a whole lot safer and is often what you find in safe or mild acid based wheel cleaners. It will not be as effective but it will still be really very good. I might use this on paint if forced but, again, I wouldn't if I could avoid it.
You then have weaker acids like
oxalic, acetic, lactic or citric acids. The latter two are pretty safe, they find application in things like chemical skin peels so I would probably have those as my go to acids here. Oxalic is used in cheap fallout removers but it should still be used with care. For example of use see this
Toyota guide. Make careful note with regards to the baking soda step, this is important for the long term health of the paint, even if many in the UK are ignorant of that fact.
As a final suggestion, you could try the
finishkare paint cleaning system. I don't know what acid is in this but it claims to be safer than oxalic and, more importantly, finishkare are expert enough to have included the important neutraliser.
Whatever you do, make sure you neutralise when done (baking powder or most APCs will do it). Although you are unlikely to see damage as soon as you apply, acidic residues can do harm at a level invisible to the eye and can manifest months or even years in the future. Whilst cheap and nasty valeters can ignore this and realise that damage will be impossible to be blamed on them, as detailers I am sure we will all agree that we should work to the highest standard.
All the best.