PROFESSOR KAROL SIKORA: The King wants to go back to work. Here's the surprising things I'd advise him as a top cancer specialist...

The King is itching to resume royal duties and remains 'hugely frustrated' that his recovery from cancer is taking 'a little longer' than expected, according to reports quoting his nephew Peter Phillips.

It is only two months since we learned of the monarch's diagnosis, and so you may expect me, as a consultant cancer specialist, to urge a more cautious approach and an extended period of convalescence and rehabilitation.

In fact, I'm all in favour of the King resuming his royal duties but this bit is key: only as long as he feels up to it.

Anyone in the King's position should rest when they need to, writes Professor Karol Sikora. But I don't believe it's a good idea to have too much time to sit around moping

Because during my nearly 50 years working in cancer care, I have seen countless patients feeling as right as rain at the start of their treatment, only to find themselves overcome by fatigue by the end of it.

The thing is, we live in a world where everything is available or done instantly, and time has become a precious commodity – and this is at odds with recovery from any illness. Cancer treatment especially can take months, if not a year or more, to come back from.

That said, the speed at which anyone recovers from cancer diagnosis and treatment will always vary enormously depending on the type of cancer, the treatment programme and the individual state of health and mental resilience of the patient.

There's usually an operation to recover from – which in itself can be hugely tiring as the body reacts as if to a trauma and prioritises the expenditure of energy on the healing of tissues.

Then may come chemotherapy or radiotherapy. Treatment designed to kill off tumours and cancer cells inevitably inflicts damage on tissues throughout the body. And this can impact the metabolism, leading to uncharacteristic tiredness which can last six months to a year after treatment ends.

Fatigue is the most common side effect of most cancer treatments and is often the thing patients find the most disruptive, and the greatest limiter to a return to 'normal' life. And this is going on at a time when a patient has to be constantly going to and from hospital.

If you work through this exhaustion, what would happen? Add to that nausea which may impact appetite, and it's easy to see why some do need a lengthy period of recovery and why good sleep and maintaining a healthy diet becomes an incredibly important part of any recovery.

Don't forget the King is 75 – an age when the turnover of cells is slowing – which means his recovery may not be as prompt as that of a 30-year-old, say. But counter to that is that men and women in their 70s these days are generally much healthier than those who lived 20 or 30 years ago, and they are better able to cope with cancer therapy. What's more, drugs and treatments are a lot gentler than they were, with fewer side effects than they once had.

Charles pictured reading cards and letters sent by well-wishers following his diagnosis

The Princess of Wales released a video last week in which she announced her diagnosis 

Aside from the physical considerations around recovery there are the psychological ones too – having cancer can be mentally exhausting.

A very difficult-to-measure impact of any cancer journey is the way it affects the mind and the spirit – and this can be exhausting too.

We doctors can sometimes be accused of becoming so focused on the technological procedures involved in diagnostics and treatment that we lose sight of the fact that each patient is a human being with their own ups and downs.

Probably the biggest psychological barrier most people face with cancer is the never-ending uncertainty: treatment is inevitably a series of steps, each leading to uncertainty.

Some people cope much better with this than others.

I believe one of the toughest challenges is being forced to face the fact that no one lives forever. Of course, objectively we all know this, but most of us go through our lives in a state of comfortable denial.

Then, with every scan and test, the cancer patient is forced to face the possibility that maybe this isn't going to work – a challenge that can be difficult and tiring.

So anyone in the King's position should rest when they need to. But I don't believe it's a good idea to have too much time to sit around moping and feeling miserable.

Far better, in my opinion, to get back to your normal life structure if you feel able. If you enjoy your job, there's no doubt that doing something you love really can help re-build your self-confidence once more, as facing the unexpected with cancer can knock your self-esteem too.

The busier you are, the less time you have to worry and become inward-thinking.

A graduated entry back into work is probably just what King Charles needs. Better still if those managing his diary allow him time for complementary therapies such as massage, acupuncture, relaxation therapy or yoga.

Although the clinical evidence is fairly weak to support them, research shows that anything that helps you deal with stress can improve your quality of life, relieve depression, anxiety, and symptoms related to the cancer and its treatment.

Everyone handles the psychological impact of cancer differently, and, in my experience, those buoyed by a supportive network of loved ones, friends and family tend to cope better.

When I consider the situation being faced by King Charles and his daughter-in-law Princess Catherine, I'm predict both will get through this stressful time well.

And when they both finish their treatment, I urge them to celebrate: to book a holiday or, at the very least, open a bottle of champagne!

Whatever your background, it's very important to have something to look forward to.