A global Eurail pass covers all participating railway companies in 33 participating countries.
The Eurostar from UK to mainland Europe has limited number of seats for pass holders and popular departures are sold out weeks, and sometimes months, in advance. Just so that you know.
That's confusing as the UK is not listed on the list of 33 countries.
That's confusing as the UK is not listed on the list of 33 countries.
It is listed under Britain or Great Britain for the network of England, Scotland and Wales with a separate country listing for the network of Ireland including Northern Ireland.
Virtually all trains in Britain (and Ireland) are valid with a global pass and reservations are NOT required for anything other than sleeper trains,
The main places you are likely to encounter in UK where Eurail is not valid is London Underground, Docklands Light Rail, and a few regional tram or metro networks.