Hi buzzz
I also don't have a copy of TG20 which is really the starting point.
However, it is "common knowledge" that insurers find all sorts of excused not to pay out, but I don't know how much of that "common knowledge" is actually a myth that could be easily blown up when the insured choose to select cheaper insurance options that come complete with lots of caveats.
So, part of the issue is to look at the conditions on the insurance policy!
But depending on the level of damage it might be more cost effective for the insured to take the financial hit and consider whether to go for a more robust policy going forward.
As is the norm on these Forums there is a problem with your photo - I can't open it and this may be the case with for other readers.
But to try and answer your specific QQ:
1. Should there be foot plates at the end of the standards on the sloped roof to add more stability to the scaffold?
YES.
If this is a scaffold e.g. erected around a gable (whether or not an extension of something built up from the ground) the vertical standards should be supported on metal (or similar) base plates (typically 150mm square) with the base plates in turn supported on sole boards (usually scaffold boards) to spread the load - suppose this is a slated roof the load bearing down via a 150 x 150 base plate will split the slates underneath. All this assumes that the roof structure is capable of supporting the load exerted on it! Which takes us back to a design.
2. Should there be toe boards on the property side of the scaffold boards?
As I can't see how this scaffold has been constructed difficult to answer. However if there are gaps on the inner face of a scaffold built up from the ground through which materials could fall and injure someone below e.g. at an entrance, then YES.
3. Should there be stop end boards at either end of the scaffold boards? If so, i assume this would exclude where the gate is?
In simple terms there should be at least top rail, mid rail and toe board at every edge from which people and materials could fall and injure someone below EXCEPT where this is not reasonably practicable.
4. Should scaffold boards be tied down when strong winds (such as storm Noa) are predicted?
5. What checks should be done during high winds, e.g. visual inspection, tying down of boards, further risk assessment?
Taking these two together, this is the equivalent of "Man at Work" signs on the roads except higher up.
So there is a standard which explains the various ways of preventing the temporary road sign from being overturned or displaced, which most usually is does by placing 11kg sand bags on the frames for the signs.
So, the standard dictates how much weight is needed depending on location. Less in places where it is generally not so windy, more in places where the winds are OFTEN higher.
Same principle applies to your scaffold. It should be designed with weather in mind and what that means will vary according to the Season, but storms in April in the UK are far from uncommon and Noa wasn't particularly exceptional.
So, the insurer's argument seems to be possibly along the lines of this being down to an "Act of God" but Storm Noa was predicted well in advance so there could and should have been a plan to deal with higher wind conditions than may have been initially envisaged in the DESIGN that should have been done - "TEMPORARY WORKS" with a TW Designer, TW Coordinator and TW Supervisor (and I am guessing that none of these were in place!)
Hence the plan includes e.g.
(a) cross one's fingers and hope it's OK - common but not generally recommended
(b) take down part or all of the scaffold
(c) put in additional precautions, which might include tying down boards, doing extra inspections etc etc.
6. With the scaffold being so close to a public highway (a road on the other side of the wall), should other precautions be taken?
That's down to risk assessment. Guidance in HSG151.