I work in the NHS, and fall under the 1 in 3. Get 9.5% + time and a half for the time, rounded up in 15min intervals. Works well enough for me, it's quite a tidy little sum extra per month. I would like more, but it's actually the highest on call pay offered in the agenda for change scheme from what I could see. They originally offered 3% !!!!
When on call on the week day, I cover 5.30pm to 8pm, and weekends is 8am to 8pm support. Basically we have to provide 8-8 support everyday for walk in centres, the prison and various other services that pay for our support!