Deliberate mistake: 9/6/10: When Lucas and Jade are getting into the car, look at the road sign behind them. Lucas is driving down a one way street the wrong way. Also the camera light is reflected in the side of the car.
Deliberate mistake: 21/10/08: Jack was giving Darren a driving lesson. Just after Tanya and Lauren got into the back seat of the car, the camera angle changed. As Darren turned the corner into Bridge Street, the driver of the car changed, as he was now much bigger than Darren.
Answer: Albert Square is a set in the BBC studios in Borehamwood, on the north side of London. The trains, to the best of my knowledge, are simply a bit of the old TV magic. As far as the extras go - it's not difficult to get extras in reasonable numbers through agencies.
Tailkinker ★