I was intentionally looking at the 1.5 because i thought the 1 litre would be under-powered. Is this the case?

Whether or not the 1.0 is underpowered for you will depend entirely on how much power you feel you need. I've seen it mentioned often on the forum in the past, scepticism on how or if a 1.0 could power a car the size of a Golf (or Octavia). To me, the size of the engine isn't relevant, the power and torque figures are, and IMO, the 1.0 has plenty for most.

If you tow a caravan, regularly have a car full of people and luggage or always have to be in front of any other road users, perhaps not. But for most folk, in most circumstances, I wouldn't see the 1.0 as being something to worry about. Perhaps a test drive though?.

When we swapped our 1.4 150PS TSi Superb last year we were equally concerned about the kangarooing and managed to get 3 long test drives (Passat and Superb, 2 were in the same car, kept Superb overnight) in an attempt to confirm the situation either way. All drives were in auto's (its what we were buying) and all were from stone cold (when the issue was said to be worse). Happy to report no issues at all but we did not care for the combination of gearbox and engine (especially in the Superb) so we decided they were not the cars for us.

Can also report that the Fabia 110PS hatch we have is really great but to be honest I would not like to drop from owning a Superb and have the Fabia as my only car. Space wise the Fabia is a match for the Golf Mk's 2 and 3 we owned, cars we lived with as our main car between 1986 and 2003. Performance from the 110PS engine is excellent and economy is about 49 mpg average over 3 years, better than the Golf 1.9 TDi 90 we had. Would I want a bigger car than the Fabia with this engine, could not say for definite without driving one over a long period but its my gut feeling that we have been spoit with the 1.4 TSi's, you would need to get a good long drive over all road types to ensure you would be happy.

Main problem with the 110 PS is supply, used ones are not exactly everywhere (we struggled to get a test 3 years ago) and new ones were discontinued last year. The new Fabia is out later this year (bigger and supposedly better) and the 110 PS should back.

But in the meantime why not look at a Scala. Slightly bigger than a Golf (much bigger boot) and available with the 110 PS engine and the 150 PS 1.5.

Going back to the issue of whether a Golf 1.0TSI would be underpowered, I started thinking back to when a worked at a VW dealer in 2000. At that time, apart from the VR5, VR6 and GTI 1.8t, the most powerful Golf was the 2.0. This had 115bhp and 170Nm of torque at 2400rpm. The 110bhp 1.0TSI in the Golf makes its 200Nm of torque from 2000-3000rpm, and is more or less the same weight as the 2.0.