Online Applying Vietnam visa from Spain

Where to get my Vietnam visa – Vietnam Embassy in Spain or UK

I am Spanish passport holder and planning to visit Vietnam for 20 days, so I know that I will need a Vietnam visa. And I must apply via the embassy as I will travel to Vietnam by bus from Cambodia. But my question is that, do I need to apply for Vietnam visa at Vietnam Embassy in Spain or can I apply for Vietnam visa at Vietnam Embassy in London, UK as I have 2 weeks there, near the embassy.