Associate
This is true.If a 'relative' took £100k out of their bank as cash and gave it away, how would the tax people know who it was given to?
However, it is my understanding that details of any transaction, linked to a personal bank account, over £20k are automatically sent to HMRC. So they would be aware you withdrew £100k. If then, by chance, your family members start depositing more than £20k into their accounts it isn't rocket science to work out what has occurred.