Many thanks for your reply.
Budget: I would like a bike under a £1000, if I need to spend a bit more to get my main requirements, then so be it. I would like it to be not too expensive as I fear it might get stolen, or it the battery might no longer work after a few years.
Style of bike: I would like to sit upright, like you see on the picture on the website on the right for Kalkhoff . There should be a fairly low crossbar, so that it does not look like a mens bike.
Range: I'd say about 30 miles (with occasional hills) . I currently have an Urban Mover from Halfords which only allows about 15 miles, with 1 steep hill of about 0.5 mile and slight inclines for the rest of the journey (from Marlow to Nettlebed). I had to purchase an extra battery to allow me to cycle longer.
You are right about limited off road use. I occasionally ride on dirt roads but find that with normal city bike tyres this are fine.
A rear battery is fine, the battery must be lockable so that when you leave it on the bike when going in a shop, you don't have to take it with you all the time.
The panniers I have are something like:
http://www.internet-bikes.com/index.php?p=117&id=11620 and fit on any normal bike rack.
I find that in the descriptions of the bikes, my main requirement - being that I want to have the choice to not to use the battery when the terrain is flat/be able to use the bike easily if the battery is flat - does not seem to be in the descriptions.
If you can give me a couple of brands/types of bike you can recommend, I would be grateful.