Who Is Striking? How Wednesday 21 December's Walkouts Will Affect You

It is the strike nobody wants. Union leaders, the government and NHS leaders all say they do not want the ambulance strike to go ahead on Wednesday. But it will - there is no hope of a last-minute deal to avoid it.

The action in most of England and Wales will involve paramedics, control room staff and support workers.

Some 750 members of the military have been drafted in to help.

The most life-threatening calls, including those for cardiac arrest, will not be affected.

This is my latest daily briefing, with lots of useful information.

Some 10,000 members of the Unison, GMB and Unite trade unions across most of England and Wales will take part in the walkout. The East of England will be the only service unaffected.

The start times and lengths of the walkouts vary between ambulance services, but all will last between 12 and 24 hours.

Ambulances will still be sent to the most life-threatening calls - known as Category 1, which includes heart attacks. But it is up to each NHS Trust in consultation with the unions to decide which calls are responded to.

Patients who are seriously ill or injured, or whose lives are in danger, are being advised by the NHS to call 999. For all other healthcare needs, the NHS is advising people to contact NHS 111 online or via the NHS 111 helpline, or to contact their local GP or pharmacy.

Out on many of the ambulances will be members of the armed forces. But their role will be limited - they won't be sent on call-outs involving critical care and they won't be providing any clinical care.

Members of the Household Division who are being drafted in say they feel "nervous" but also "honoured" to be helping out.

Watch Make Sense of Strikes on iPlayer and find out more about why people are striking and whether industrial action works.

This year NHS staff in England and Wales, including ambulance workers, have already been given an average increase of 4.75% - with a guaranteed rise of at least £1,400 for the lowest paid.

Unions representing ambulance staff want above-inflation pay rises to prevent, they say, a recruitment crisis.

Civil servants in the Public and Commercial Services Union (PCS) - including driving examiners - are striking on Wednesday.

Until 24 December, the walkouts are in north-west England and Yorkshire and the Humber.

From Wednesday teatime, we will have another strike briefing for you - looking ahead to Thursday.

But, with Christmas edging closer, we know it's one of the busiest and most chaotic weeks of the year for many people. So bear the following in mind for the week ahead:

On Friday 23 and Saturday 24 December, members of the Communication Workers Union (CWU) will walk out on two of the busiest days for pre-Christmas deliveries.

There is ongoing disruption and some localised strikes throughout this week and well into next, but a national strike of RMT members is due to start at 18:00 on 24 December until 06:00 on 27 December. Network Rail says that most train journeys will end at 15:00 on Christmas Eve.

Even on days when strikes aren't happening, many passengers are facing reduced services due to an overtime ban by the RMT at 14 train companies - the ban runs until 2 January. On some lines that means services starting late and finishing early.

How are you affected by the strikes? Are you taking part in strike action? You can email: haveyoursay@bbc.co.uk.

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