Hi --- Providing care home needs are not currently expected in the near foreseeable future and you are not reasonably expecting to within the next six to twelve months, then placing these investments as you intended into trust for your Grandchildren would not be viewed as deprivation of capital by the authorities, should these care needs eventually arise.(left unprotected in your control, it will be considered as your capital).
You should seek the advice of a member of staff at the Halifax who could arrange this for you so the assets are released in accordance with your wishes, i.e. on your Grandchildren reaching maturity or upon your death, whatever.
What this does is place the money in a protected trust legally outside of your control, with a trustee appointed (Parent or someone you trust) as per the name......who would be responsible for administering and making sure the beneficiaries receive the money as and when you wish for in accordance with the terms you place in the trust.