Firstly, please note that Sweden is NOT in the Eurozone. The unit of currency is the Krona. Consequently, Swedish banknotes can be changed anywhere.
Here in Belgium, old BEF notes can only be exchanged for euros at the National bank in Brussels. They will not be accepted anywhere else.
As far as exchanging Austrian schilling and Italian lira notes in London is concerned, maybe the national banks of those countries would exchange them. If you have sufficient value in those currencies to justify the cost of travelling around, telephone calls etc, try contacting them.
If you only have a relatively small value of notes, put them in one of the foreign currency collection boxes which you will find in many airports. They will go to various charities.
I think that it might be a good idea to exchange your Swiss and Norwegian money in Europe rather than wait till you're in Singapore.