How to be a lifesaver: After MP Tobias Ellwood tried to save hero policeman Keith Palmer, our essential guide to helping treat the wounded

A bomb in a confined space can lead to shrapnel injuries and serious burns. Joe Mulligan of the British Red Cross cautions against trying to remove sharp objects embedded in flesh.

'They might be blocking a major artery, so if you remove them, it could result in catastrophic bleeding,' he says.

Burns should be doused in cold fluids. 'It doesn't have to be water. It could be beer or lemonade from the pub,' says Joe.

'Do not remove clothing if it is stuck to the skin because this could cause further injury.' 

If the victim is unresponsive and not breathing, lie them on their back and make sure their airway is open by tilting back the head and pushing up the chin.

Start performing CPR (see panel far right). If there is someone else available to help, ask them to staunch blood flow from any wounds by applying pressure.

'Don't remove their clothing, which could put them at risk of hypothermia. Instead, cut or tear their clothes so you can see the wounds, then apply pressure using your hands, a scarf or T-shirt,' says Emma Hammett.

If the victim is unresponsive but breathing, first attempt to staunch the blood as above. Once blood flow lessens, roll them gently into the recovery position (on their side, with the top knee bent, and with one hand cradling the face — see illustration above). 'Make sure that they are lying on the injured side. This will prevent fluid entering the uppermost lung,' explains Emma Hammett.

Meanwhile, she says, 'If the victim is still standing, get them to sit or lie down. They could collapse at any point, injuring themselves further.'

Keep the victim warm and calm to reduce shock. Do not give them anything to eat or drink, as they will almost certainly need emergency surgery. It might be tempting to tie a tight ligature around a limb. However, there is evidence that wrongly using a makeshift tourniquet can make blood loss worse.

'It should only be used in a small number of cases where bleeding is catastrophic, and if direct pressure is not working,' says Emma.

Severe bleeding may not be immediately obvious if it is internal, warns Alan Weir, of St John Ambulance. 'Be aware that a small puncture wound might be the only sign that an organ or major artery has been hit and the patient is bleeding to death.' 

If someone isn't breathing, you may need to perform cardiopulmonary resuscitation (CPR). 'To check for breathing, ensure the airway is open by tilting back the head and lifting the chin,' says Emma Hammett. 'Spit on your hand and put it close to the victim's mouth. It'll feel cool when breath is expelled. They should be breathing at least twice every ten seconds. If not, start CPR.'

There are two types of CPR: hands-only and mouth-to-mouth. You should attempt mouth-to-mouth only if you are trained and feel confident to do so. Otherwise, use hands-only CPR.

Hands-only CPR

Lie the patient on their back. Place the heel of your hand on the patient's breastbone at the centre of the chest. Place your other hand on top of that hand and interlock your fingers.

Using your body weight, press straight down 5-6cm. Take the weight off your hands and allow the chest to return to its original position. Repeat 100-120 times per minute.

Mouth-to-mouth

The same as above BUT after every 30 chest compressions give two 'rescue breaths'. Gently tilt the patient's head back and lift the chin. Pinch the nose. Seal your mouth over theirs and blow steadily and firmly for one second. Check their chest rises and give another rescue breath.

Continue with the cycle of 30 chest compressions followed by two rescue breaths.

CPR on children

Alan Weir, clinical director at St John Ambulance, says children over one should have the same first aid as adults, with adjustments for size. 'Use one hand rather than two,' he says. 'Breaths can be shallower so as not to over-inflate the lungs. Giving CPR to babies is much more delicate, with just two fingers used to apply pressure to the chest. The infant's whole mouth and nose are covered with the first-aider's mouth, giving small breaths at regular intervals.'

Move them as little as possible to avoid further damage to the spinal cord. However, if their airway is in danger, you may need to 'log roll' them into the recovery position. This requires three or four people to carefully roll the person while holding their head, torso and legs, so their spine remains in alignment.Avoid cradling the head if you suspect a spinal injury. If you must move them from danger, ask others to help 'log roll' them (as above). 

Serious injury can swiftly lead to a life-threatening complication called circulatory shock.

'This isn't something you will necessarily see if paramedics arrive on the scene very quickly, but it may set in over a longer period of waiting for help,' says Joe Mulligan.

Some people will become confused and weak as a result of low blood pressure. Other warning signs are clammy skin and cold extremities as blood is diverted to the core organs.

'Use coats or blankets to keep the patient warm. Reassure them and keep them calm. Try to prevent any further fluid loss by applying pressure to bleeding wounds, but don't offer them anything by mouth.'

Broken bones are very painful but are rarely life-threatening, and treatment should be left to the professionals, says Alan Weir.

'If the ambulance is a long way off, it sometimes might be useful to straighten twisted limbs to restore blood circulation — although this will be very painful for the patient.'

Dislocations look terrible and are painful, but again, don't intervene. 'Doctors use X-rays to guide them when they reset dislocations so they don't trap blood vessels or nerves,' says Joe Mulligan. 'Instead, make the patient comfortable until help arrives.'