RC - if you're ever travelling by train, I can recommend
How to travel by train from London to Spain: Madrid, Barcelona, Seville...
The bloke on there really loves his trains and there's journeys mapped out from London to just about anywhere in the world.
For Madrid, you'd be looking at leaving Monday around 1400 hours, arrive Madrid 0900 tuesday. Then the return on wednesday leave 1900 hours, arrive 11.28 into london on thursday.
Looking at about £300 round trip from Newcastle>Madrid.