The very idea of Hitler winning the Second World War is a terrifying one - and in new BBC1 drama SS-GB, an adaptation of Len Deighton's 1978 novel starring Tom Riley and Kate Bosworth, we see what Britain might have looked like if that had been the outcome. In the show, there are swastikas lining the streets, Wehrmacht soldiers guarding Buckingham Palace and the Queen Victoria memorial on The Mall has been knocked down.
So how did showrunners transform London into an outpost of Nazism? Radio Times spoke to executive producer Sally Woodward Gentle and discovered it was no easy feat.
"We felt we just couldn't hang up swastikas so we did all the Nazi banners in CGI, " says Woodward Gentle. "You just can't do that for real and it's much more sensitive to do digitally. The main thing we really wanted to keep to a minimum is that horrific symbol. We had to put huge amounts of thought into this and had to think about the most sensitive way to do it. I think London would have been one of Hitler's jewels in the crown so he would have really made Nazi imagery key all over the city. But our priority was being sensitive to the public when filming in London – so CGI was used for the swastikas."
CGI was also used for the the bomb damage done to the palace. Given how extensive the destruction is in the show, it was far more cost effective to do it that way.
"We filmed on the Mall but used CGI to remove the Victoria Memorial, which we imagined the Nazis would have dismantled. In our imaginary world we imagined that the Nazis wouldn't have wanted a symbol of the British Empire there and were planning to replace it with something else."
A few of the road signs emblazoned with "HALT!" and Nazi imagery were real – but they were only used when the set was closed, which meant that fewer members of the public could catch sight of the filming. The Spitfire, seen right on the Mall, is real – but it was towed in, not flown in.
Between takes, all the actors playing German soldiers had to cover themselves up with ponchos. “This was particularly sensitive," says Woodward Gentle, "so we made sure that their uniforms weren’t visible to the public walking by. When their uniforms were visible we closed the set to minimise the number of people who could see."
"We put a lot of signs up saying 'filming is taking place' and lots of people in the locations department were on hand to talk to any passerby and tell them what we were doing, " says Woodward Gentle. "We really did try to keep as much stuff hidden as possible but in London you can’t completely close a set – people will always see what you’re doing. People were fascinated – they thought we were filming a superhero movie.
"It’s really difficult – you make a decision to shoot in London but then you’re like 'Oh my God, we’ve got to shoot in the incredibly busy capital city and not let anybody see..."
SS-GB is on Sunday 19th February at 9pm