LONDON (Reuters) - Royal Bank of Scotland (L:RBS) said on Friday its Natwest unit would pass on in full a 25 basis point cut in the Bank of England base rate to its standard variable mortgage customers."We're passing on the base rate cut in full to our valued mortgage customers on our standard variable rate," RBS said in a statement, a day after the UK central bank halved the key borrowing rate to a record 0.25 percent low in a bid to shore up Britain's wilting economy."We have been the fastest growing large UK bank with net lending growth of over 20 billion pounds in the first half of the year - higher than any other bank. We're open for business and ready to lend responsibly to homebuyers up and down the country."