DISASTER!!!!!
Please learn from my mistake and always ensure you overtly purchase compatible paints! I suggest that testing a small area is a good idea too.
It turns out that the Frosts chassis paint is not compatible with self etching primer - if I had read the tin, I would have known a lot earlier, and would not have introduced a couple of days worth of extra (and very intensive) labour.
About 15 minutes after I applied the stone chip this morning, I noticed that there were a number of patches looked very wrinkly. At first I thought this was just an area where I applied it slightly too thick, but oh no, that wasn't even close. Upon agitating the stone chip, the top coat simply lifted off the etch primer - my heart sunk - I was majorly gutted. The odd thing is that the top coat looked spot on, and was resistant to being abraded, which told me that the key between it and the primer was good.
After considering a number of options, including hanging myself, I decided that the best thing to do was to grind off ALL of the paint and start afresh from bare metal. This did however mean that I would lose the galvanised zinc coating. This is inconvenient, but not a show stopper - the reason I went for a galvanised finish was to protect the inside of the chassis, which is where the rot usually stems from. The zinc was always going to be painted over - I now just need to place more emphasis on maintaining the painted finish. The inside will still be treated with Dinitrol once the exterior has been sorted.
Despite spending many hours today sorting out the mess I have created, I have nowhere near finished. I have taken the front/underside of the chassis back to bare metal, etch primed, and then, because I'm not sure if I'll top coat before stone chip or not, have tested a small patch of stone chip straight onto the primer. I'll speak with U-Pol to see what they recommend as a top coat, just to understand what my options are.
All in all, I'm seriously hacked off with myself!!! That said, sh1t happens - just got to get on and sort it out now.