The big drop in the value of the Pound (GBP) this week, due to uncertainty over the possible future independence of Scotland, definitely has an impact in organized crime, especially drug trafficking organizations. Many money launderers are required to keep a portion of their clients' illicit wealth, secure, but on hand in cash, to cover large narcotics purchases, and also potential attorneys' fees, should a clients be arrested, as well as cash to pay for a bond, where pretrial release is available.
Criminals are businessmen too, and they do not take kindly to a substantial drop in the value of their large ready cash stash, especially when they are concerned that there is a possibility of a further decline. In that case, a change to a more stable currency may be warranted, to preserve value.
If I was a "financial advisor" (money launderer) for a DTO in the UK, I would certainly consider exchanging my cash for US Dollars, at this time. Should you be approached, this week or next, to change a rather large amount of Pounds into Dollars, from an entity with an urgent request, I suggest that you press the seller for details about Source of Funds. Is the response too vague for you ? Then decline the business.