UK Public sector pensions strikes Police to join up to 400k .
Hundreds of thousands of public sector workers are taking part in a 24-hour UK-wide strike in a dispute with the government over pension changes.
The government says current pension schemes are unfair - and unaffordable because people are living longer.
But the unions say members are being "robbed" and will have to pay more and work longer for lower pensions.
Meanwhile, the government has said that walkouts by prison service staff in England and Wales are unlawful.
Among the public sector workers taking part in the 24-hour strike are civil servants, NHS workers - including paramedics - border force staff and lecturers.
Around 32,000 police officers are taking part in a protest march against cuts, according to Metropolitan Police estimates.
Union leaders say up to 400,000 workers will strike while the government says it is more likely to be half that number.
Mark Serwotka, general secretary of the PCS union - which estimates that an "overwhelming majority" of its 250,000 public sector members are on strike - told BBC Radio 5 live the cost of pensions was falling as a proportion of GDP.