Private equity and infrastructure investor 3i said the value of its portfolio will be lower at the half year due to falling stock markets."We have continued to invest selectively and taken the opportunity to realise assets at attractive prices," said chief executive Michael Queen."The economic outlook looks increasingly challenging and falling stock markets mean that the value of our portfolio will inevitably be lower at the half year despite an overall solid trading performance."The majority of 3i's funds are invested in private equity. It recently invested £134m in Action, a Dutch discount retailer. Other investments include the restaurant chain Giraffe and the camping equipment retailer Go Outdoors.