How do you determine the maximum current demand on a ring circuit

Most, if not all, electricians here answering questions are from North America, and a re not familiar with UK wiring. I know enough to be dangerous, from what I can find the internet.

Calculating demand can be as simple as adding up the total load of each device.

I do not know if there are any demand factors allowed by the UK electrical standards.

This link seems to be a forum similar to AMHD that deals with UK wiring:

Electrics UK Forum - DIYnot.com - DIY and Home Improvement