Thanks guys. They offered him a �10/month contract but these days (just retired) he won't be using his phone as often so I still reckon it will be cheaper with PAYG. Wasn't too sure about the details but I'll pass the info on. Many thanks guys!
keeping in mind that a lot of PAYG top ups have a time limit on them I'd be tempted to stick on contract at �10 a month.... if he is not using it then at least it's a easy to budget amount
and if he stays on contract if the phone ever breaks he is entitled to a free upgrade