Your right it looks so out of place. Apparently it covers over 5 acres and can hold 10,000 for prayers. That's why there's always problems on the road on Fridays because the roads just cant handle that amount of people.
I have no idea how they got planning permission for it but you and I know what goes on at those meetings so that probably was a formality.
At the time it was built it was the largest Mosque in Europe but I just don't get building it in Morden. Southall yes but not Morden.