Thinking about this, I recall a holiday in Venice where the travel arrangements were a Eurostar to Paris, followed by an overnight train from Paris to Venice. Only the first leg was bought in London. The train to Venice was bought in Paris. My recollection is that this was cheaper than paying...
This suggests purchasing and paying for the holiday before leaving the UK. Am I alone in thinking that the best deals in Europe can be found by turning up at your destination and then looking for accommodation?
I would usually book travel from the UK though.