I support the consensus. You should be driving at speeds appropriate to the conditions and available information on potential hazards.
But to be fair to the OP, there was surface water and the incident took place around dawn.
This is probably the worst conditions. A good driver would compensate for the increased danger by driving slower.
Although the highway code gives a stopping distance of 40ft for dry conditions at 20 mph, the reality is that tyre/road grip is less good in the wet.
A rough rule of thumb would be to double the stopping distance (thinking distance remains the same), so overall stopping distance should have been around 60ft (18m).
The OP says the hazard was around 50m beyond the blind bend.
This should have given ample time to slow down or stop in a safe and controlled manner, even with a tailgater behind.
Unless the actual speed was closer to 30mph, in which case the theoretical stopping distance in the wet would be around 40m.
To achieve that deceleration, one would really have to hit the brakes quite hard, and yes, there might be a risk of a tail-gating driver failing to respond in time, possibly resulting in a rear-end impact.
In fact, the Highway code stopping distances are based on old-technology tyres; drum brakes and ignore brake assist technology and traction control/ABS.
With modern tyres, emergency brake assist, traction control, disc brakes and other modern paraphernalia, the Highway Code significantly over-estimates stopping distances in the dry. Furthermore, the very best tyres have comparable stopping power in the wet as in the dry.
In short, given the situation as described, there should have been plenty of time to come to a safe, controlled stop with no risk of rear-ending.
If the collision was unavoidable, then one has to conclude that the situation may not have been as described in the OP