Patch of paint has cracked.

[BlueMonday]

I noticed a patch above the rear door, near the roof of the car when the paint has cracked.

I am not sure what caused it to happen.

What is the best way to deal with it? I am no expert at rubbing down and painting but wondered if there is something that I could apply to it to stop it spreading?

[degzi]

It looks like historic damage, it may be that it has had a bad repair in the past or something like stone chips, there's small bubbles around the cracks.

Tbh a body shop might not charge that much just to tidy it up. I got a full door respray for £60

[Lord Voltermore]

I agree ,it looks like a  roof dent or something was repaired with body filler, but with inadequate preparation.    And the rust bubbles suggest it needs stripping back to bare metal  over a larger area than the more obvious cracks.   Just filling in the cracks and spraying over  would not be satisfactory IMO as the underlying rust spots could get worse, if not treated  ,leading to perforation and weakness.

Extending the area  a bit shouldnt add  much to the cost as the basic skilled preparation, refilling and spraying metallic paint and clearcoat will be necessary anyway.   

[BlueMonday]

I bought the car when it was 3 years old so it is possible that it was damaged and repaired before I bought it.

There is no sign of a dent that I can see though.

I wondered if it could be caused by bird droppings?

[Kremmen]

I also reckon it's a badly repaired dent and with the current heat the expansion and contraction has caused it to fail