Well, Humbrol, as the Humber Oil Company, had been going since 1919, originally making paint for bicycles, and making model paints from the 1950s.
I've used them since about 1960 and, as I mentioned, they were the best in the World at one time, bar none.
But, since the various take-overs by various groups, including Borden, they were put out of business in 2006, and the paint, still under the Humbrol brand name, which was bought-up with the Airfix and other brands, is made elsewhere.
Some of it is OK, but it can be hit and miss, and many times I have been unhappy with the inconsistent 'quality'. That said, some recent paints seem to be much better, so it's possible that it is now made to a better standard, but only time will tell.
I'll admit, I do like Model Master paints, although some of their colours seem slightly 'off' in shade, compared to the 'real' colour, but not by much.
Oh, and I find that, unless Model Master paints are stirred really well, like any enamel, they will not adhere as quickly as they should, and take a lot longer to dry, if applied by brush, and must be thoroughly stirred before thinning for airbrush use.