Hi the Eurail One Country Great Britain Pass allows you to use almost all trains only in Great Britain (UK without Northern Ireland).

The Eurail One Country Ireland pass allows you to use trains in the Republic of Irland and Northern Ireland. 

If you need a pass for both Countries, you can buy an Eurail Global Pass valid in 33 countries in Europe.

Thanks! I think that too

Passes for UK/GB tend to be quite expensive-it all depends on how much you want to travel-what works out best. The difference with EUrail global is minimal. For ONLy in Rep. IE there are also a few local passes for its trains-but all lines only go to/fro Dublin.

In both countries RES is not needed as such,except the 2-3 NightTrains, but on some major lines advisable-can do for free when there @ counter of major stations or online. GB is still plagued by strikes=huelga every now&then-hope that is settled once you get there as Porteno!

Welcome to the UK (and Ireland). If you need any advice on where to visit just let us know.

The rail network in the UK is extensive, but I suggest you consider carefully whether a continuous pass might be better than a flexi (x days in Y months) and paying for extra short journeys, as even local flexible fares can be expensive, even on short journeys.

Also do not consider fixed saver fares because they are very strict on only valid on the named train, and on the day fares will cost far more than the daily cost of your pass. 

Also the freedom to hop on and off our trains with a pass means you can really visit just what takes your fancy. There are very few trains not included in a Global pass so you can easily cover all 4 corners of the UK by rail. Also as Mcadv points out reservations for those trains offering it are free and easily sourced. so your only cost is your pass.