How the fck they think 8 people could have been lost at sea when it's a straight line swim in decent conditions with bright coloured hats and probably 30-40 safety canoes, paddle boarders and jetskis is beyond me. Oh I forgot sometime in the 90s we removed the right of anyone putting on any sort of event to apply what used to be called common sense. With participants fully capable of refusing to enter after making a personal judgement call on safety it's just indicative of scapegoat Britain.
That said it was made abundantly clear in the race pack and in the briefing that you HAD to check out regardless of when or where you stopped - even though IMHO after many years with ZERO losses it's complete overkill. It said you may be liable for search and rescue costs if you fail to comply I'll wager the cost of the search and rescue that clause won't be applied!
For the record the 'administration' was some people with clipboards manually taking the numbers of people in the finish area - at best that's prone to significant human error for something so critical. How about give everyone a chip (or if that's too expensive then just get them to tick a box when they sign up agreeing to pay if they don't check out) and tell them if they don't return it they'll be charged £30 - that'll do it. Mind you realising that modern society requires a forfeit to get people to do anything they may find a little inconvenient would require a modicum of common sense ;o)
As you were.