Why would you think that is true? Here in the USA we eat less red meat than we did 45 years ago, and are way less healthy. NHS and the USDA make all kinds of boneheaded dietary prescriptions that are terrible (eat lots of grains, eat trans fats, avoid eggs, avoid butter).
Since the 1970s, at least:
* Americans eat less red meat and more white meat than they used to in the 70's.
* Americans get fewer calories total from meat than they used to, yet eat way more plant material (hint: carbs) than ever before. https://imgur.com/a/LgqUMJz
* Americans and Brits are way more overweight than ever before, with the obesity "trend" starting in the late 70s or early 80s. Obesity should concern you, it kills 10 times the people that the US opioid epidemic does (300K deaths/year vs 30K deaths/year), but culture makes it much harder to take 10 times as seriously. Or talk about at all for that matter. What's a minute increase in bowel cancer comparatively?
Why fear (unprocessed) red meat in 2018, and why on earth listen to the NHS on the subject? Are people who listen to NHS guidelines actually healthier than people in the 1970's, who ate more red meat?