I also did a set of long exposures with the 10 stop ND filter. These were all the rage a few years back but seem to have gone out of favour with photographers now - although when I show them to non-photographers they still get the "WOW!"
Let me know if you lan to visit @Douglas McMann and I'll tell you how to get down to the river rather than being limited to the tourist viewing platforms. Don't expect any facilities or visitor centre. It burned down in 2013! Mohammed Al Fayed owned it.