I have off-ice skates as well, but finding somewhere smooth enough that isn't over-run by kids is difficult
I know what you mean! Having skated on wheels for years, I am always searching for flat, smooth places to skate. Even in urban areas, it is surprising how bumpy, uneven, twiggy or sloping most surfaces are. People who don't skate on wheels think almost all asphalt is smooth, whereas most is quite unpleasant for small wheels. The bigger the wheels, the less of a problem it is. I skate on 80mm wheels which are better than the off ice skate wheels for rough surfaces. A friend of mine who figure skates uses 90s and another friend uses tri skates with I think 110s or 100s and she's annoyingly nimble on them.
I've been chucked out of a few car parks. Supermarket car parks Sundays after 4.30 could be an option, but currently I drive for an hour to skate at Emirates Stadium. For the winter I am looking at hiring a local hall for myself and a few friends. Prices seem to be reasonable - £25 to £30 an hour which if you only find a couple of others is pretty good value if you consider you'd have the place to yourself. Ice is much lovelier but it is expensive and at present I just don't want to have the hassle of all the restrictions.
For anyone in or near London, Hyde Park, Battersea Park and Emirates Stadium are all good options.
Happy skating all.
I'm getting smooth block paving on my drive so I can at least do cones...