The actual speed limit on that roundabout is an interesting issue! It's debatable, but the most accurate 'guidance' I can find is that it should be the speed of the majority of the approach roads — how you're supposed to work that out, sat in your own approach road, I don't know. The one in question is almost certainly 30-40 mph, which is about 50-65 km/h. In theory, some roundabouts have a 70mph speed limit, although they'll be very different from the one in question.
Disclaimer: UK driver, detest roundabouts.