If you have a low budget, England (London in particular) will be very expensive so limit your time there. You will do a little better in Ireland, but not by much. For 3 weeks, I would concentrate one week in England, one in Ireland and One in Scotland. London is great for a few days then, if you like biking and the outdoors, consider renting some bikes in the Cotwolds. Head up to Edinburgh from there and maybe fit in Gasgow if you have time. At that point you will have to fly to Ireland. Dublin for two days then check out the area around Kerry for some amazing natural sites. If you have time (but I odn’t think you will) Belfast is an awesome city. Ask a black cab driver for the “tour”.

As for partying and drinking, all of the cities mentioned have a really great nightlife. Look around for an open jaw flight into London out of Dublin if you want to save some time.

I did a smilar tro over 2 weeks a couple years ago and it was awesome, I’m going back in early May next year. Other suggestions in addition to mim’s…

1) Bath – spend 1-2 days it’s extremely nice and a great base to go see Stonehenge if you’re interested.
2) You’ll probably find Glasgow is much better for partying than Edinburgh because it’s cheaper and more of a student town.
3) If you love adventure, I would consider a tour of Scotland’s highlands, I can’t recommend any tours because I haven’t taken any but I’m defiantly doing this when I go back.
4) If you’re interested in cathedral’s I highly recommend Salisbury, the cathedral is incredible.
5) If you wanna stay near the Temple Bar district of Dublin, I suggest Avalon House. It was a pretty good hostel and once you learn your way around, is a pretty close to stuff.
6) The St. Christopher’s Inn is an amazing hostel in Edinburgh with an excellent location and I found it was great for meeting people.

If I think of anything else (and I probably will), I’ll defiantly post some more.

thanks so much guys that was all very helpful

I’d suggest you start by flying into Shannon, then taking a bus to Dingle, a small village that attracts a lot of artists and traditional musicians. Then take a bus or bus train to Dublin (either way its a whole day in transit), and from there move on to England. I wouldn’t rent a car in Ireland, it is expensive and most of the roads are primitive. You can hire a guide very reasonably to get to some of the remote sights. In Dingle, the eco tour is an excellent adventure, a boat ride through some amazing scenery with perhaps the best guide I have ever heard.

In Dublin, Temple Bar (or barf, as they call it) is the entertainment district, packed with tourists, but still entertaining. You can buy a ticket on one of the on/off buses to get oriented and get around (the ticket we got was good for the day we bought it and the following day). I thought the Guiness tour and the Book of Kells were not a good use of time; both are packed and you spend hours in line. You can take the local light rail to Howth for almost nothing, and enjoy an oceanfront fishing village with excellent food and scenery. Try fish soup; it is excellent.