Thanks for the help
I shall keep looking around, well I shall try anyway (I'm not very good at shopping, although baby shopping is far more fun I must say).
I've asked a few stores and most have said to go for the 3 wheelers on the rough ground. Mind you none have really been as helpful as the first place I went (Baby Mode in Epping - they were great!). I asked about the 3 wheelers tipping and they have all said that they don't - after reading that bit I thought oh no maybe I'd better go 4 wheels after all.
Thanks again and I shall keep a-hunting!