Civil servants picket outside Pentonville Prison

Staff in Jobcentres, benefit offices and prisons are taking part in the 48-hour walkout in separate disputes.

Many benefit offices across Britain will stay shut as strike action continues, union officials have said.

Public and Commercial Services union (PCS) chief Mark Serwotka said members had walked out because they were "fed up with being undervalued".

'Poverty pay'

The dispute involving 90,000 workers at the Department for Work and Pension concerns a pay deal due to be settled in July 2003.

The PCS claims many of its members have to survive on "poverty pay".

The PCS is considering legal action over the imposition of a new pay performance system and has called on government ministers to intervene in the disputes.

The union has warned it will take the department to the High Court unless it withdraws the scheme, complaining that the "unilateral imposition" was a breach of contract.

But the DWP's management have said the pay offer on the table is a "substantial" one - worth an average 5% - targeted towards more junior and less well-paid staff.

Prison disruption

Administration and support workers at the Prison Service are striking over a separate wage dispute.

The walkout by 4,500 staff could disrupt the transfer of prisoners.

Outside the public sector, thousands of railway workers are to vote on strike action in a row over pay and pensions.

Around 7,000 signalling, maintenance and station staff at Network Rail will be balloted by the Rail Maritime and Transport union.