Town Centre is Church Street in Twickenham.
Yes, they are outside the Eel Pie pub in Church Street at the beginning.
Bearing in mind that they lived in an anonymous town, I thought that there were surprisingly few inaccuracies or flaws, although I was surprised that the 7.41 had a trolley service, as announced when they got on the train on the first morning, and also there was a scene at Waterloo after the train had arrived where there was a cluster of people waiting to get through the ticket barriers but nobody walking along the platform towards the barrier from further back in the train.
I very much enjoyed the programme even though its not the sort of thing I usually watch, and I had a bit of a chuckle thinking about how uncomfortable some people who had had affairs must have felt.