- 1. Tamiya acrylic paints can't be brushed.
2. GSI/Creos Mr. Color Leveling Thinner causes paint cure times to be long.

You can slow the cure time using other retarders. I've tried GSI's Mr. Retarder Mild (love the name), Golden's, Windor & Newton, and even glycerin. All make brushing better, but are nowhere as good as Tamiya's brand retarder.
For my recent Fujimi Type 10 build, I sprayed Tamiya JGSDF colors for the main camo and brushed the road wheel rubber with Tamiya acrylics thinned as above. It took about an hour to paint all the rubber. I used the same thinned/retarded paint from start to finish. No lifting. No rollover.

Can you tell which paints were sprayed and which were brushed? This is a 72nd scale model and sizes are greatly magnified.
Regarding GSI/Creos' Mr. Color Leveling Thinne, this is a lacquer thinner. It's basically the same as their Mr. Color Thinner but with a retarding agent added. This is to keep Mr Color paints from spider webbing when it is sprayed. The retarder keeps the paint from drying before it hits the model surface. Actual drying time for these paints is minutes. After spraying Mr Color lacquers thinned with Leveling thinner, I can mask and spray another color within 15 minutes. Mr. Color may increase drying or cure times for other paint lines, but not the ones for which it was designed.
I suspect you probably have difficulty obtaining Mr Color paints in the UK. They are available from many Hong Kong based mail order shops (maybe MDC?). So if you can't get the paint or don't want to bother with international mail order, why should you use Mr. Color Leveling Thinner? That's simple, this is a fantastic thinner for Mr Hobby and Tamiya acrylics when spraying. Unless I'm looking for special weathering effects using Tamiya acrylics, I use Leveling Thinner. The paint sprays better and it dries harder. Another advantage for using these GSI thinners is that they are safe to use on plastic without using any sort of barrier coat. They will not etch the plastic like most lacquer thinners. They are really good for removing paint without damaging the model.
Mention is made in one of these paint guides of the odd colors in the Tamiya Acrylic line. These paints match JPMA standards, so they are shades Japanese modelers need when doing cars and trains.