I find closer pitching makes for a good atmosphere on site.Not so sure I’d really want to reduce the distance as on some Continental sites we have visited you can seem much closer to your neighbours and more closed in. Though I’ve never worried about the fire aspects. Whilst modern vans are no doubt more fire resistant than the old 1930s construction that you quote, they do burn very rapidly if fire takes hold.
Close enough to chat, close enough to share a beer.
However, there is a financial issue with the very wide spacing on UK sites, revenue per acre is very low, much lower than overseas operators can generate in the same area.
So we have two options, ever increasing U.K. prices, (already very high), or sites close.