Irremoveable stain on white paint work

[Mpm95]

Anybody any ideas about what this stain could be and how to remove it? I have already used a heavy compound but have had no success. Thanks.

 

[PDK]

Have you tried a clay bar?
Has it been painted do you know?

 

[Mel]

Had this on my roof. No idea what caused it, may be a spray wax build-up. Tried everything. Citrus Pre wash, tar remover, fall Out remover, polish, none had even the slightest impact.
In the end as @PDK suggests, clay bar was the only solution. Almost had to scrub the car with it.

 

[Mpm95]

Really? I thought clay done very little in terms of removing stains like that, ill try and see