Before you leave the UK, go into the Settings menu, select General, then Network. 4th box down is Data Roaming, turn this to OFF. This will prevent your emails etc from automatically updating abroad.
If you keep the Wifi button ON, then anytime you go into a free wifi spot, it will try to connect to it and you can then access email,facebook, etc for free.
Personally I like to have my phone with me abroad as it means I can send texts (much cheaper than voice calls), eg if I lose my DH 
Ensuring the Data Roaming is turned OFF will mean you NEVER have to worry about those huge bills we keep reading about in the DM!
(nb you dont actually need to have Data Roaming turned on at home anyway, as your mobile provider's signal is what powers the internet connection for accessing email etc; I tend to have mine turned off all the time and when abroad, I occasionally turn it on for a few seconds if expecting an important email in a wifi dead zone. I do know that I will get billed for this but it's a calculated expense IYSWIM)