If you have 4 grandchildren and have left them each £46000 that has to be kept in trust until they are each 21yrs (between 3.5yrs and 13.5yrs left). Is it better to invest in one trust between them or one each?
And why would there be a 50% tax liability for them anyway?
A joint one is less paperwork - fewer tax returns, etc
It's 50% tax because chancellors don't like trusts. If you were to consult a professional advisor he would recommend a trust and investment strategy to avoid much of that tax.