It's shite. I'm surpised at just how low it is, and with a pathetic £5.5k personal allowance, I can do £6k in OT next year. At this rate, that should see me about 5 months worth of OT. Past that point, I ain't going to bother, as the government aren't getting any more out of me.
I take it it's a sliding scale, so you only pay 40% on anything past the £34.5k mark?