Dazzling sun - what do you do?

Part of my daily commute is in sun glare at this time of year... I flip the visor on my cap down, as I would the sun visors in a car, and use bright 'daylight' lights. And try to get away from the lights fast and get well out in front - aided by a couple of speed cameras set to 20mph, not too difficult.

pray, grip the handlebars a bit tighter, what else can you do ?

sometimes if its really bad Ill stick a flashing rear light on,hope its enough to catch the eye of the driver that a shadow doesnt.

but Im often stuck on roads at certain times of the year where it becomes an issue, and there arent alternate routes to take, not that often you plan them anyway, it could just be that day at that time the sun is at the perfect alignment with the road, and its not a nice feeling for sure.

I commute by bike and regularly face the situation of low sun essentially blinding me during autumn and spring.  Not so worried about oncoming traffic as they can see me perfectly, it's the cars approaching from behind on virtual autopilot that are the real risk.  

What I do (but i'm not in the UK so the following may not be realistic) is either minimize my time on roads shared with vehicular traffic by taking a detour that passes over gravel/separate cycling paths or leave earlier/later.

I won't ride recreationally under those circumstances, just too risky.  If you can't see where you're going, it's time to dismount.

If you are struggling with low sun when you are riding the bike, that car with a dirty windscreen coming up fast behind you is not good news.
By today's standards you should be riding with lights, but you are competing with the sun, so will probably lose.
Get off the road if you can, stop for a coffee, take a side road.
This is not a good time to take prime position, get over to the left. If I'm not going to be seen, I would rather not be seen in the gutter. Sit up to make yourself as big as possible.
None of this will make much difference.
My best advice is Hope for the Best.

As I'm not commuting I just try to avoid it, either by riding at a different time or in a different direction. Rear DRL for a modicum of safety.
In my younger days of renting places to live I always factored it in by trying to live east of where I was working. That comes from an incident early in my driving career when I almost hit someone due to being dazzled.

I watch my mirror carefully and am ready to bail.

I think the answer depends on whether you accept that x% of drivers are incompetent and y% of that x% are wilfully incompetent. Unfortunately, there are something like 1% of drivers who take deliberate risks, in the main, these are people whose luck hasn't yet run out - they perhaps are ones who think their judgement is brilliant because when they overtook into oncoming traffic they didn't have a collision and they don't perceive that was because all the surrounding traffic took avoiding action (not that they wouldn't chase down a driver who did that to them). The risk takers will simply hope the road ahead is clear.

Drivers may not be as blinded by the sun as a cyclist as a sun visor is a fairly effective tool.

So, when I am in that situation, I know I have a bright daylight flashing light and I take up a strong position and regularly check my mirror and also give serious consideration to where my bailout points are. The other thing is to shade my eyes - and if I am still struggling to see having done that, then I am wondering how effective a sun visor would be. Serious problems are morning easterly roads on a rise where the sun can sit right on the horizon.

If I was a BMW or Audi driver I would, of course, put my foot down to quickly get out of trouble.

Low sun particularly when it's likely to be combined with wet roads is something that I avoid like the plague.
If those conditions are likely then it's either off-road only or a dammed good thrashing on the turbo.