I don't usually dive in to these sorts of threads, but on this one I'll bite, so here goes.
...why would a cycle club decide to ride out of a very busy beach resort up a really steep and winding A road at lunchtime on a Saturday in August
Because it's not a Motorway so they're allowed to ride there?
...and on what planet would any cyclist think it OK to undertake the cars trying to weave safely through the gaps in the traffic?
One where filtering is permitted by the Highway Code, i.e. this one. You do imply they were trying to do it safely, after all
Come on guys, you genuinely are putting lives at risk . Where’s the risk assessment on that cool idea?
Was it definitely a club? Your jumping to the need for a Risk Assessment could be misconstrued as "'elf and safety gawn mad, guv"
Train on the hill midweek when it’s quiet by all means but mid August Saturday lunchtime??
Maybe they didn't realise they apparently aren't allowed on that road on Saturday lunchtimes in mid-August?
Why put everyone at needless risk? You should not be there...
Really? On whose authority? Again, maybe they missed the sign saying they're not allowed there?
...but I bet you’d blame the car driver if it all went wrong. And yes, I am a runner, long distance cyclist, motorcycle rider, and car driver.
Sorry, but this smacks of "I can't be racist, I've got black friends" to me.
Rant over? Nearly. If a teacher put a KS4 group in that situation they would be instantly dismissed but apparently it’s ok to choose that route cos you’re all adults? I know, I am a KS4 teacher. You better be certain you have no teens riding out with you
Slightly tangential, but most employers who don't want to end up in an Employment Tribunal don't instantly dismiss anyone these days. It's suspend and investigate, invite to disciplinary, hold hearing, communicate decision and offer right of appeal.
All of that said, if it was a club and their choice of ride was just adding to the Daily Mail-fuelled culture war against cyclists, then perhaps a reasoned email to an officer of the club would be a more productive course of action? We all see fellow cyclists doing dumb shoot at times which does none of us any favours, but personally I draw my anger threshold along the lines of the law - i.e. RLJ, pavement riding, lightless nijaing and littering etc, not just "being out for a ride on a busy Saturday in August". YMMV