Founders and investors in QoS Networks, an Irish telecommunications company, are suing Warburg Pincus, the US buy-out group, for damages of $650m (€531m), claiming a breach of fiduciary duty. Warburg Pincus is counter-suing, claiming the founders deceived it over performance.

The claimants allege Warburg Pincus pushed the firm into bankruptcy by blocking additional fundraising in 2001, Bloomberg reports.