According to this article a full tank of gas in the CT200h will yield around 52mg (at least according to my math). The source is not clear and it seems that Lexus is being rather tight-lipped so far, but if this is accurate, I think my next car won't be a Prius after all... 'Sporty' emphasis for new Lexus hybrid - Telegraph
The EU fuel economy test cycle is weaker than the US EPA cycle and tends to produce larger numbers. The current Prius gets 72.4mpg (Imperial) and the new Auris Hybrid 74.3mpg (Imperial) on this test cycle. 621 miles divided by 9.898 imperial gallons is 62.7, worse than my second-generation Prius. Of course the reporter could have misheard or mis-transcribed the value. If it's in the British press it'll be an EU test result.
If driven carefully, I don't why it shouldn't be able to get 50mpg, esp. if ppl can get 60mpg in the Prius. It's more likely to be rated in the high 40s.
A good guide for fuel economy to us here is the magic g/km figure. The 2010 Prius gets 89g/km whereas the older 2003-2009 Prius was rated at 101g/km. The article states the new Lexus CT200h will be below the 100g/km range, which allows for important tax benefits over here. I'd be expecting fuel economy to be better than the older Prius but not quite as good as the 2010.
