iPad Data Plan Recommendations (UK)

Hi everyone, does anyone have any recommendations for good value for money data only plans for an iPad in the UK.

I’m currently on 3, and it’s great, except, if I max out my data allowance, they let me go 100mb over, sting me massively for the pleasure, and then cut me off!

Cut me off when I reach the cap with no charge, or continue to charge me massively for using over my allowance, but allowing me to go over by just enough to get a (relatively) massive bill, but not by enough to do anything useful is just really really customer service.