Coal attacks stainless steel in three ways, chlorine attack, sulfur attack, and, most importantly, iron particle induced pitting corrosion. There is a lot of iron in coal exhaust flyash. The small iron particle allows a pit to occur in the stainless liner which (together with the low o2 level in exhaust gasses) continues to rot without allowing the replenishing of the passivation layer.
If you have a masonry stack, lined or unlined in decent structural shape, you are far better off than with stainless (or with a stainless liner). We have had at least two people on this board with documented stainless liner collapses (in addition to the many cases on this site of stainless failures) causing flue blockage, lack of draft and CO entering the home. Probably the safest thing you can do with a coal appliance on an otherwise sound stack (lined or unlined w/ tile) is to remove or not install a stainless liner. If you're concerned about a stack w/ mediocre draft, fix the stack properly and extend the height, don't add a stainless liner.
Interestingly enough, this iron particle pitting corrosion also happens with fuel oil - especially in situations where an older tank has a nice layer of algae. The algae and water allow microscopic iron to enter the fuel stream, the burner, and pass through the flame into the stack. I've personally seen it destroy stainless w/ fuel oil in less than 15 years.
As far as masonry chimneys in england; no, they're not rotting out in 20 years. In fact, there are numerous unlined and tile lined stacks that have regularly been used with high chlorine/ high sulfur british coals for well over a century with little internal deterioration. The brits used a lot of lime based mortar, and, when combined with high chlorine, high sulfur coals, certain unlined flues after a century or so have deteriorated, especially when later connected with a gas appliance. Yes, the brits did use a lot of native coal that was extremely high in chlorine (higher than almost anywhere else in the world) and very high levels of sulfur (5%+).