1.2 Sportback

The new A3 Sportback with the 1.2 engine is not available in Germany (where you would expect to see it first), so I suspect it will not be offered as an option in the UK.
 
Strange as I read somewhere that this was going to be one of the initial release engines.
 
According to Audi Latested News dated Feb 26, 2013

Ordering is possible now for three-door versions, and will become available for five-door Sportback versions in the summer. First deliveries of three-door versions will begin in May. More details available at:

Petrol or diesel? New 57mpg Audi A3 TFSI makes the decision even harder < Latest news < About Audi < Audi UK

With regards performance the following is stated:

Thanks to ample 105 PS and 175 Nm outputs, economy isn’t the only string to their bow – the six-speed manual version reaches 62 mph from rest 0.7 seconds quicker than its predecessor at 10.3 seconds without compromising efficiency – CO2 output is now 13 g/km less than before at 114 g/km.
 
Finally a petrol with good mpg, but more than 65bhp! However, if the engine is made to be lightweight as the press release suggests, it might be a very noisy and ticky engine!