So long as they're hardened off properly, I'd risk it - they tolerate up to 10 degrees of frost anyway, its the damp in winter that kills 'em... In fact, I've been potting up geraniums today for someone here in West London... but I have hardened them off over the last week. The one I wouldn't risk yet is Impatiens...

I live in Lancashire and 2 weeks ago I put out my Geraniums that I'd overwintered in the conservatory. They appear to be doing well.

As Bamboo pointed out, it's too much water that causes problems. Geraniums like full sun and a dry condition. They don't need a lot of water and too much water will cause the stems to rot.

Did mine today.