By Steve Slater and Aashika Jain LONDON (Reuters) – Royal Bank of Scotlands systems crash that left more than 1 million British and Irish customers unable to withdraw cash or pay for goods on Monday has revived concerns about the resilience of the state-backed banks technology. The three-hour outage on one of the busiest shopping nights of the year could cost RBS millions of pounds in compensation and comes as Britains regulator is threatening to fine the bank for the collapse of its payment systems last year. The regulator has been scrutinizing the resilience of banks technology amid concerns that outdated systems and a lack of investment could cause more crashes. From 1830-2130 GMT on Monday, RBSs cash machines didnt work and many customers trying to pay for goods with debit cards at supermarkets and petrol stations, buy goods online or use online or mobile banking were unable to complete transactions.