Just thought I'd let people know about this. Was on a 12 month contract sim only bill pay plan with Three which ended last week. Was costing €31.34 a month. Rang them up with the intention of switching to prepay for €20 a month.
Agent offered me a €10 per month discount for 12 months (now €21.34 pm) to continue on the bill pay plan, so went with that. It's better than the prepay option as you get a better calls to other network allowance, plus the EU roaming allowance is better too.