In this episode, with nearly all of St Mary's 297 beds occupied, the hospital must discharge patients before any new ones can be admitted.

While the hospital tries to discharge patients, new ones continue to arrive. Peter Lai, a 60-year-old retired software engineer arrives at the hospital for a lifesaving operation on an aortic aneurysm in his chest. St Mary's is a centre of excellence for vascular surgery and this is one of the biggest operations they carry out. It's taken two months to co-ordinate the diaries of the expert team, led by consultant Colin Bicknell.

But unless the hospital staff can clear a bed for him, Peter's operation won't go ahead.

Discharge Nurse Sister Alice Markay, is trying to discharge a homeless Polish man, but until she can find a translator to explain what will happen to him when he leaves St Mary's, the man will remain in a hospital bed. Alice says: "The pressure that's on the NHS, you worry about it because the walls are not elastic and the demand is high… But you have to look after the patients, whether they come from Buckingham Palace or the park bench."

Another patient the hospital needs to discharge is 91-year-old Dolly. After breaking her ankle, Dolly has been in hospital for three weeks while she waits for a place in a rehabilitation centre. Dolly laments: "They're so short of beds… but then I have to have somewhere to go where I'm going to be safe. I feel guilty because I've got nowhere else to go".

A woman from Nigeria recovers in the hospital after going into premature labour with quadruplets, having fallen ill on a flight. Only three of her babies survived the dangerously premature births and they are now being cared for in Neonatal Intensive Care.

She receives a visit from the hospital's overseas officer Terry, whose job it is to prepare her for a huge bill. Because she is not a British resident, she must pay for the care that she and her babies are receiving. The cost of such specialist care quickly tops £100,000 and looks likely to rise to half a million pounds during their stay.

Terry explains that, despite her distressing predicament, it is a legal requirement for the hospital to collect the money the NHS is owed.

"We have to start raising invoices on a weekly basis. She has three babies in ICU. So that's £20,000 a week for each baby, plus her own charges as well. You have to distance yourself emotionally, otherwise you wouldn't get the job done."

The woman is just one of a number of overseas patients who are receiving life-saving care and from whom the hospital must now try to recoup money. Although emergency treatment given in A&E is free, non-UK residents who are admitted to a ward have to be billed.

Terry also needs to charge Sonia, a 56 year-old woman from the Philippines who suffered heart problems while visiting her sister, a UK resident. Cardio-Thoracic surgeon Rex Stanbridge saves her life, but she suffers complications and needs a bed in Intensive Care - costing thousands of pounds per day.

In 2015/16 the Trust's overseas patient charges were £4 million, with Terry's team managing to collect £1.6 million. Despite carrying a credit card machine to take on-the-spot payments, Terry finds it hard to get many patients to pay up.