It seems to me that you launder the money. It would take ages, but you randomly ask people if they have change for a 20 (the pics here showed that it was all 20s). Now you have 4 fivers or 2 tens...either way, so poor unsuspecting schmo (an American tourist most likely) will now find himself in Scotland Yard explaining why he bought an Underground ticket with a stolen 20. You fan out across the UK and do this, you are clean.
Again, doing this for 40M lbs is a lot, but you get the idea...
Just my (not very) criminal mind at work.
Hey, Bace...can we work this into our photographer murder mystery?