There is a big difference between "out of proof" or "refinished" in merry England, Greg. Out of proof is against the law to sell, refinished is considered much more like maintenance there, and is completely acceptable.
I've heard arguments pro and against sleeving, and the hit a sleeved gun will take is significant. I won't buy one, period, I know a few others who fall in the same camp, and a few more who would buy for .50 on the dollar, or so.
I don't do sleeved guns, so, figure 100% of value erased on that. However, a well maintained Brit boxlock, with nicely reblacked barrels and freshened checkering should sell for at least as much as an identicle, original gun needing same. The Brits are much less weird about original finish than Americans are, and you tend to find guns that have had regular service all their lives.
Best,
Ted
