RBS challenges investors on costs as rights issue trial nears

By Kirstin Ridley and Andrew MacAskill LONDON (Reuters) - Royal Bank of Scotland is demanding that thousands of shareholders suing the bank over a 12 billion pound ($15 billion) cash call in 2008 prove they have appropriate insurance cover to meet the hefty risks of a trial now slated for May. RBS said the RBoS Action Group, a 27,000-strong group of retail shareholders backed by around 100 institutions, had so far declined to give the bank assurances that they had adequate legal expenses insuran