It's a public health issue. What people - mostly men - see in pornography, they copy and repeat in the bedroom. There should be no normalisation of strangling one's partner. It's dangerous and harmful.
Despite having little understanding of the law in the U.K., I can confidently say that strangling someone without their consent want already illegal. There's no need to criminalize the consensual version of it.
Consent needs to be adequately informed. Plus it is an ongoing process, and being strangled affects one's ability to continue providing consent due to its effects on the brain and body.