I dropped a tin of paint this afternoon. Fortunately this occurred
outside. The paint is oil-based primer (red oxide). The surface is
some sort of concrete. How am I supposed to remove this?

1. B&Q suggest white spirit but I cannot see this working after the
paint has dried.

2. Steel brush attached to power drill?

3. Nitromors?

4. My favourite - flame thrower (as used for clearing weeds)?