By Tom Bergin LONDON (Reuters) - Internet retailer Amazon.com Inc. will be called back to the British parliament to clarify how its activities in the UK justify its low corporate income tax bill, two lawmakers told Reuters. Amazon will follow search giant Google, which attended another grilling by parliament's Public Affairs Committee (PAC) over its tax affairs on Thursday. A Reuters report earlier this month raised questions over Google's earlier assertions that its UK-based staff don't sell to customers. ...