When Westpac increased its standard variable mortgage rate by 20 basis points last November it was to maintain its return to investors following a A$3.9 billion equity capital raising.However, the bank's financial report for the six months to March shows that the margin impact of the rate increase was fully offset by competitive pricing in the mortgage, business, personal and institutional lending markets and higher short-term wholesale funding costs.Changes in term wholesale funding margin cost the bank one basis point of margin.The margin was improved three bps by improved customer deposit spreads.Overall, on a cash basis the net interest margin rose three bps to 2.14 per cent, compared with the September half.In the current half the bank faces further funding pressure, as competitors have started to increase deposit rates. Comparison site Mozo reported that six deposit-taking institutions increased term deposit rates last month and four institutions raised their at-call rates, with rates rising by as much as 50 basis points.