If you've previously used the same combination of primer/top coat on the same original car paint with good results, then I'm more inclined to now go with what Will2CV says - primer applied too thickly and not dried off enough (more likelihood in this cooler weather?). So, under the seemingly-dried top surface of primer, the rest of the primer underneath is still 'soft'. Top coat then applied and dries quickly contracting as it does and mobilising the primer underneath which isn't as stuck to the original paint as it should be - since it ain't stuck, it moves.

A theory...!

I must confess I think you maybe correct there, I don't think two hours was quite long enough, ah well good job I've managed to get a weekend off work! Thanks to all, I shall update once I've done my second attempt!

That is a paint reaction. If you've rattle canned it and someone has used some oil based or synthetic paint on the wing that'll react with the solvent in the rattle can paint. You may get away with building up very thin layers of primer and letting them dry well, or strip to bare steel.

You've also got islands. After you've primed spray a guide coat of black or another dark colour. All you need to do is very lightly mist it. Then rub down lightly with 800 grit wet or dry. The edges will show up as dark rings.

not a bad rattle can job though i always cock it up

Isn't that mark where a side repeater has been blanked off?

I'd imagine so; the edge of the filler needs to be so thin it is translucent. Otherwise it'll show through the paint.

Wheels look good!

Yes I'm afraid it was rattle can but I'm doing the rest as professional as I can with the resources I lack, as far as I'm aware there was never a side repeater there as it doesn't need them, glad you like the wheels russ, they'll look good when they're finished!

If youre using rattlecans one of these is handy .....

It clips onto a large aerosol like this .....

It's the next best thing to using a genuine air powered spraygun [and it works in exactly the same way]

FWIW .....I think you've put too much primer on too quickly and then follwed it with the topcoat too soon.
If it was my car I'd leave it for a week [or there-abouts] ......and then rub it down with 600 & 1000 grit W&D so that its flat ....and then put one coat of primer on,followed by several thin topcoats.
An electric lamp [garage inspection type] with a 100w or 150w bulb placed in the wing [on the wheel] would help provide a bit of heat to dry the paint out quicker.
It also helps to have your rattlecans reasonably warm .....24-36 hours indoors at "room temperature" should do the trick this time of year.

hth
Terry

ah i like that, how do i get hold of a 'rattle can trigger'? ill google it... i managed to get a whole weekend off (amazing considering i work in retail!) so providing it doesnt rain (fingers crossed!) ill get cracking