Could you recommend an electric van or a petrol Euro6 model?

Are there any electric panel vans, equivalent to a Citroen Relay or similar, available? If not, as I suspect, what would you recommend in the petrol vehicles, that meet ULEZ requirement of Euro 6. I ask...

Why are there so few long wheelbase standard height vans on the market?

I am about to buy a van for self-employed courier work. After looking into different types of vehicle, I have decided on a Transit Custom L2H1. I like the Transit Custom for it's comfort and accessories...