This site says it is accepted at 160 countries worldwide, and I see no reason to disbelieve them:
http://www.standardchartered.com/pk/personal/c redit-and-debit-cards/en/visa-shopping-card-pl us.html
Don't forget that the Visa debit card gives you similar protection as a Visa credit card, so I think it is much better than Maestro.
"Visa debit card
A Visa debit card offers significantly better protection for shoppers. Their scheme is called Visa Debit Chargeback and any bank that issues a Visa debit card has to comply with the scheme.
You can claim money back if the goods you buy are damaged, or the product or services are not delivered.
There is no limit on what you can claim. But you have to claim within 120 days of the date you expected the goods to be delivered or the firm going bust."
http://news.bbc.co.uk/1/hi/programmes/working_ lunch/7593369.stm