Newcastle and Edinburgh-based Virgin Money, which is being bought by Clydesdale and Yorkshire Bank owner CYBG for around £1.7 billion, said on Thursday its underlying profit before tax increased by 10% to £141.6 million in the half year to June 30. However, Virgin Money forecast a drop in full-year banking net interest margin (NIM), a measure of lending profitability. "The ongoing competition in the mortgage market and differential between front and back book margins has, as expected, impacted our banking net interest margin," said Virgin Money. The lender expects a full-year banking NIM of about 1.62%, lower than the 1.72% reported in 2017, as it reported a drop in first-half margins. In its o utlook for the rest of the year, Virgin Money said: " Our central planning scenario for the rest of the year assumes a continuation of resilient economic conditions …