I've been playing around with an extract of the OSM data to compare the length of roads that have been plotted with the statistics on road lengths published by the Department for Transport. The DfT publishes figures for each local authority, and recently people have been adding a lot of local government boundaries to OSM. So it has become possible to compare the two.
I still can't make this work for all local authorities. That's partly because the data is incomplete, and partly because of mistakes in the way I have collated the data. However, thanks to help from the Talk-GB list, I am begining to get plausible figures for quite a lot of England and some bits of Wales.
It's an interesting exercise - I am learning a lot about Postgresql databases and the Postgis extensions. I haven't finished. There is still work needed to plug the gaps and improve the accuracy, and better examples to aspire to, like this. But I thought an initial view might be timely, even though it is incomplete.
Anyone who hasn't booked their holidays yet can already see that there is work needed on the map in Cornwall, and quite a bit in Cumbria, Northumberland and Norfolk. And Bracknell.