Start in Spain, travelling by train down to Andalucia, perhaps stop off at Madrid for a bit. Then train back up through Spain to the south of France, stay there and do some cycling tours. After this, train to Paris for the day, then train to the Netherlands, look around Amsterdam/Rotterdam for a while, then train from Amsterdam to Germany (Frankfurt, Munich, Stuttgart), then to Berlin. Then back through the Netherlands, possibly stop off at Belgium for a while, down into France, then ferry from Calais or Le Harvre back to England (most likely Portsmouth).
Travelling Europe the summer before university!
Still looking for flights? You can have flight experts compete against one another to find you the absolute best and cheapest flights.