Just the trip from Madrid to London would require an overnight and a change of train station in Paris. Total travel time of about 18 hours and the least expensive economy class ticket would be about $215 USD one-way. That doesn't even include Murcia to Madrid or London to Manchester on either end! To make the evening train from Madrid to Paris the OP would most likely need to leave Murcia the afternoon or evening beforehand so it would now be a three-day trip and probably require an overnight hotel stay in Madrid. In this case I don't think rail is really an option from both a time and money standpoint.
And in case certain anti-sympathizers are scrutinizing this post I did indeed carefully research this information. I didn't simply pull it out of my nether-regions as has been suggested before. I would post links to various rail schedules and booking engines but you seem to have enough time on your hands so do the research yourself!
