You can’t exchange Scottish or Northern Irish bank notes in Sri Lanka. Travellers’ cheques aren’t normally accepted. Most major banks will allow Visa and Mastercard cash withdrawals. There are ATMs in major towns and cities but not all of them accept international cards.
It’s relatively easy to send funds to Sri Lanka. However, money can’t be transferred out of the country without an exchange control permit issued by the Central Bank of Sri Lanka. For further information and a contact point see this Central Bank of Sri Lanka guide.