In reply to hetaher:
you are most likely to find a cheap flight going to somewhere in Europe, rather than trying to get back to the u.k. Comet do some pretty cheap flight, but just to Spain I think. You may also pick something up form Iberia, Air France or Klm again going to be cheaper getting to their hubs rather than a u.k connection, spend a few hours on skyscanner working out the different routes. From Europe you can hitch home, or take a bus.
As far as I am aware, British registered cargo ships won't take passengers anymore so much harder to hitch rides than it used to be. the only real option for crewing yachts is from the Caribbean as that is where all the rich types spend the winter, but will cost a lot to get there from south America.
good luck!