>>>the train is also an option
. . . but not an easy one.
According to the Die Bahn website (which has rail timetables for the whole of Europe), and taking Monday 6 October as an example, there are just 4 services per day:
1. Depart at 0607, travel for 5 hours 34 minutes (with 2 changes), arriving at 1141.
2. Depart at 0745, travel for 7 hours 31 minutes (with 3 changes), arriving at 1516.
3. Depart at 1005, travel for 6 hours 42 minutes (with 1 change), arriving at 1647.
4. Depart at 1634, travel for 6 hours 7 minutes (with 2 changes), arriving at 2241.
Die Bahn:
http://www.bahn.com/i/view/GBR/en/
CP:
http://www.cp.pt/cp