With few exceptions, like the Airfix Southern Cross liner kit, the Airfix ship kits are not particularly rare having had multiple reissues over the years. The Southern Cross is valuable because it was a limited run promotional item for the company that owned the real ship. A kit in mint condition would probably sell for a few hundred pounds. The Airfix 1/600 SS France kit is maybe the next most valuable at £100-£200 on eBay because the tooling is lost and the kit cannot be produced again. Next would be the 1/600 MV Free Enterprise II. The original release of this kit was quite limited and it was never re-released. We also know the moulds are missing. Typical eBay pricing on that is in the area of £100. Depending on condition and box type I’d expect the other 1/600 ship kits to sell in the £10-£50 range and the large sailing ships in the £25-£75 range. You can find people listing them for a lot more, but won’t see many sold items outside those ranges. I'm less familiar with the Revell, Renwall, Lindberg, Hawk, and Aurora ship ranges but there are some that can sell for £100+. The best thing to do is look at SOLD items on eBay, not listings, if you want to get an idea of current value and don’t be surprised if an item sells for much less than expected. Less frequently, things will sell for well-over expectations if you get two motivated bidders. The bottom line is his collection is probably not worth life-changing money.