Boris Johnson is leading a campaign to urge Britons to lose weight and improve their health.

Here are some of the key questions around the issue:

– OK, I know I’m looking a bit chunky. How do I work out how much I need to lose?

The NHS website has a body mass index (BMI) calculator which tells you the healthy weight range for your height.

You simply input your age, ethnicity, weight and height and it calculates how much you need to lose to reach the healthy weight range.

Experts agree that while BMI is not a flawless way of calculating obesity, it is a pretty good indicator and more reliable than dress size.

You can find the NHS BMI calculator at: www.nhs.uk/live-well/healthy-weight/bmi-calculator/

– So do I need a strict diet?

Experts agree that a combination of diet and exercise is usually needed to help people shed the pounds.

But the saying “you cannot outrun a bad diet” is generally true and significant changes need to be made if you eat too much junk food or unhealthy snacks.

Your GP can help you find the solution that will work best for you.

Many people have success with traditional slimming clubs, and there are a wealth of online resources and apps to help you on your way.

It’s crucial to get started. If you’re overweight or obese, you have a higher risk of high blood pressure, heart disease, stroke, type 2 diabetes and some types of cancer.

– What are the health benefits of losing weight?

The health benefits of losing weight can be enormous.

Most people get health benefits from losing even a small amount (about 5%) of their weight if they keep it off.

In some cases, people with type 2 diabetes – which is heavily linked to obesity – have reversed their condition through losing weight.

Losing weight can stabilise your blood pressure, improve cholesterol levels, decrease the risk of heart disease and cancer, and can improve mobility and decrease joint pain.

– What about the benefits to the NHS?

Health Secretary Matt Hancock has said if everyone who is overweight lost 5lb, it would save the NHS £100 million.

Diabetes alone costs the NHS £10 billion each year.

This is mainly because of its complications, through things such as amputation of limbs, blindness, kidney failure and stroke.