Nabarro is taking legal action against a former client over unpaid fees totalling approximately £1m.

AssetCo, which manages and maintains London's fire engines, has been a client of the City firm for over five years. The firm's head of corporate Iain Newman manages the relationship.

Earlier this month AssetCo raised £16m in an emergency share placement in order to pay creditors. According to a partner at the firm, Nabarro took a lead role on the capital raising, despite not having been paid for its advice on earlier transactions.

Nabarro also acted for AssetCo on its £15m fundraising in 2009, with Newman and corporate associate Kristy Duane heading up the firm's team on that occasion.

News of Nabarro's legal action comes after it emerged that a £26m cash call was put to AssetCo's shareholders last week. The company's former chief executive John Shannon and finance director Frank Flynn have also filed lawsuits claiming that hundreds of thousands of pounds is owed to them.

AssetCo's external counsel is currently unclear. Nabarro declined to comment.