I've painted panels using Paintnuts JCC 515 Marine Blue aerosols available on eBay. Expensive at £20 a can for aerosols - but still a fraction of the cost of getting a pro to do it. The cans have fan nozzles which means the paint goes on well. Just make sure you shake cans for at least 2-3 minutes.
It took just under three cans to do two doors inside and out.
Colour match is superb and the finish is at least as good as British Leyland managed.
It goes on in a satin finish - for a factory type semi-gloss, spray it on 'wet', the nozzle a few inches from the panel with overlapping strokes, working your way down the panel, do all the edges first. It goes off quickly with an even tone and dries hard. I did a couple of coats, waited a day, keyed it with 1200 grit and gave it another couple of coats.
If you need it a bit shinier or to blend it with neighbouring panels, give it a buff with T-cut.
I thought about brush painting but this is far better. Try it, you won't be disappointed.