Can GBP be directly used in Austria

No, GBP can not be used directly in Austria. No store will accept them.

You won't have any serious trouble finding a currency exchange store to convert them to Euros though.

There are a number of reasons that a shop might choose to accept some currency.

• Obviously, they'll accept the local currency.
• If they're in an area where a relatively large fraction of shoppers are tourists from some particular place, they might accept that currency, too. Likewise, if they're very close to an international border, doubly so if, for example, tax regulations make it profitable for people to cross the border to buy alcohol, cigarettes or some other highly taxed product.
• If they're in an area where the local currency and economy are unstable, they might accept some major world currency (typically the US dollar or maybe the Euro) because it's more reliable than their local currency.

None of these situations seem to apply to Austrian shops and British pounds. Obviously, it's not the local currency, there will be many more more visitors from neighbouring countries (which was kind of the point of the Euro in the first place!) than the UK, and the Euro is a perfectly stable currency to do business in.

An enterprising individual will accept them, but I will rip you off on the exchange rate. Better off converting it elsewhere for cheap. I worked at a souvenir shop around Praterstern during my younger years and I did this numerous times.

In Vienna you might find places to get your money exchanged (some places might try to rip you off, so better be a little bit careful)

Although if you only go to more rural areas in Austria, it could be quite difficult to get your money exchanged. As I grew up in a very rural Area in Austria, I can't recall ever seeing a place that would exchange money outside of the big cities (Vienna, Graz, Salzburg...).