Scarier looking than it actually is scary. It's Steatoda nobilis, the noble false widow. As you have already noticed they are usually quite shy & skittish and bolt for their hiding place when disturbed.
Be aware of them, but they're not really anything to worry about outside. Females, like yours, tend to stick to their webs & close to cover. I have a couple indoors, as long as they're not anywhere where they may end up somewhere awkward (e.g. bedroom/bathroom) I leave thm be. Males I prefer to evict from indoors, as they wander more by nature.
Ah cheers. Thought it might be as soon as I saw it. Never seen one before, but quite amused given all the media hoo-ha that one turns up on my house a couple of weeks later. Half tempted to turn on the light it's built it's web on to help it catch some food.