Most basic requirement for me is one with a timer function and fan.
From then on it’s just a case of how much you want to pay for extra features, better heat distribution, possibly better reliability etc.
Put a cheap Belling oven in my flat many years ago that fulfilled the timer and fan requirements and was nice and black and stainless. Been a good oven and cooked food well.
Ones like NEFF, Bosch, Siemens (often the same underneath as Bosch but higher price and a bit fancier), Zanussi etc seem to be good and in the not cheap and nasty or very expensive bracket.
I don’t think you can go wrong with the Bosch here: http://ao.com/product/HBA13B150B-Bosch-Classixx-Electric-Single-Oven-Stainless-Steel-24640.aspx
Not sure if the £50 cashback is on top of the offer price. Probably is.
But plenty of cheaper ones that look okay too.