Either should be fine in the UK climate, 0W-20 gives a little less friction, and in theory, 5W-30 should give the engine a little more protection.
I've always used 5W-30 on modern engines, and according to the service invoice, Honda dealer put 'Shell Helix AG 5W-30' in the new addition to the fleet. It doesn't say whether it's semi or fully synthetic, but I'm guessing the former - seeing as people on service plans are offered pricey upgrades to fully synthetic. Cheapskates.