No, despite the sentiment on this sub it's illegal and a controlled substance and will be confiscated from you unless you can demonstrate proof that you're a business that requires it.
I was unfortunately part of an operation two years ago in which a popular UK seller was discovered by the police, and disclosed all the addresses of orders that they had shipped to in the UK. As a result, I had a few interactions with the police whereby they performed a wellness check etc and made sure I was no longer in possession of it. If you're a lone individual who can't provide any proof that would satisfy their requirements for having it they will confiscate it.
That being said, this was a one-off case where the seller was UK based, was popular in this forum, and had willingly given up the names and addresses of those they had sold to. When they contacted me, it wasn't in a "you're in trouble" sort of manner, it was definitely a "we're worried about you" and so you're likely not at risk of being in any legal trouble, althought you may have mental health services knocking at your door if you're caught.
BUT as far as I'm aware this is a rare case whereby people were systematically caught and processed by the police. I've since ordered from IC and had no problems with the police. As others have said the vast majority have ordered with zero problems, this was definitely a one off case. But as far as it being legal goes, no, it's not.
I believe this is the thread I'm referring to for the operation:
https://sanctioned-suicide.net/threads/sn-police-investigation-uk.59452/