It's worth remembering that John Lewis don't manufacture the ovens. They simply get Electrolux (who actually make them) to stick their brand name on them.
So it might be worth researching satisfaction levels with Electrolux products, to see what people think of them.
Thanks Buenchico, saw they were highly rated on the which website, but will look into it more before deciding. Off to the shops tomorrow to have a look, as present oven is not working now.