My 2 cents (although not same engine, but also a petrol EcoTSI)
Official Numbers
53/64/72 mpg
(1.4 EcoTSI is 48/60/68?)
My Experience (average MPG on car trip computer, all journeys more than 10 miles, start/stop active):
Heavy traffic in Central London: 30-35 mpg
Medium traffic in Central London: 35-43 mpg
Light (9:30 am on Sunday) traffic via central London: 45-50 mpg
I guess the above is the closest you can get to their urban cycle in real life. I'm confident if it was 3am, I can get 53mpg average in city.
Medium - light traffic outside central London on 30-50mph roads: 53-58mpg (highest ever average 60mpg)
Highway runs (65-75mph): 48 - 55mpg
My old 2.0 TDI DSG with official 55/64/70 mpg numbers did almost identical 'real life' numbers except on highway runs, it will do a lot better more like 55-60 mpg. Highest ever average 64mpg

.
So if you drive exclusively only in the city, 35-40 mpg average is about what to expect. If mainly outside of city zones with not too bad traffic expect high 40s low 50s. Even mid 50s possible.
If you want to meet the manufacturer 'official' urban economy numbers. As far as I know, the test doesn't have traffic incorporated into it. Try a run at 3am in the morning, spending long parts at consistent 30mph (Computer should show instataneous 60-80 mpg when you do), with the odd traffic lights here and there. Believe me, you will get close to, achieve or even exceed the 'official' numbers.