To consider the likelihood of ditching, the commander would need to know how many of the thousands of channel crossings by SE aircraft have ditched (with the exception of the ones that ran out of fuel).
Having made numerous long channel crossings, I must admit feeling the odds of an in flight emergency must be getting shorter and the CAA requirement has caused me to consider the issue more seriously.
In my case I consider a survival suit preferable to a life raft. I don't fancy my chances of successfully getting a life raft out of a high winger and clambering aboard, whether the aircraft remains upright or flips inverted on contact with the water.