LONDON, April 26 (Reuters) - A passenger ferry operated by P&O, the troubled company struggling to maintain its service, suffered a "temporary mechanical issue" on a crossing to Northern Ireland that required a response from lifeboats and pendik escort local tug boats.

P&O Ferries has struggled to operate a service after it fired 800 workers last month to cut costs, drawing sharp criticism from the government and sparking union protests.

Britain's Maritime and Coastguard Agency (MCA) have since inspected a number of P&O's vessels and suspended four from sailing.

Three have since been allowed to return.

P&O said following the mechanical issues, its European Causeway ferry was now continuing on its scheduled journey to the Port of Larne in Northern Ireland under its own propulsion, with local tugs on standby.

The RNLI lifeboat service said it had sent three lifeboats to assist the passenger ferry.

"There are no reported injuries onboard and all the relevant authorities have been informed," a spokesperson said.

"Once in dock a full independent investigation will be undertaken." (Reporting by William James; Editing by Kate Holton)