I thought for a moment you were a Geordie Jossi!!! Then I realised you mean a plain old 1.4 PETROL.
The S was never badged as such, but it stands for 'Standard' and is effectively the base model.
'SE' models were also never badged as such, but they represented the 'Special Executive' or 'Special Exclusive' model, basically the base model with a few luxury touches, such as leather bits (not upholstery though).
The third variant in the A2 range was the Sport and was the base model plus sporty touches, such as sports seats and quattro suspension.
There was also the run-out Special Edition model, which was a mish-mash of things, basically a parts-bin special.
Audi don't make a habit of badging their cars in this way, unlike Ford, Vauxhall etc and they also offer de-badging as a no-cost factory option.
Cheers,
Mike