Looking at the weather, I'd say that the light rain we have currently in London will go fairly soon, and probably be followed by sunshine (albeit a bit chilly) for the remainder of the day. How much this will dry the roads remains to be seen.
I don't know what Adam's attitude will be, and he knows the route, but I would suggest that avoiding any minor roads which are likely to have been significantly wet will be a good idea, since they'll tend towards a risk of iceyness.
Ice was always going to be an issue if the temperatures dropped below zero, you rarely get freezing temperatures with completely dry roads in this country.
I'm having to make all my decisions on what to take and wear now, since I'll leave directly from work, but I don't think I'm going to bother to fit the studded tyres.
I don't know where Aperitif found a figure of -12°C for Hyde Park. It may get to -2°C, but I think -12°C would possibly be record breaking!