"I would like to make provision for a third party who was the deceased’s carer and partner."
There is nothing stopping you simply gifting however much you wish to, to the carer, after you receive the money. It's your money and you can do what you like with it.
The only consideration will be if you die within seven years of giving this gift to the carer and your estate (including this gift) is subject to Inheritance Tax (IHT), (typically more than £500k if you're single or more than £1 million if you're married and your spouse has already died and left everything to you).
If you die within seven years then any gift is counted as still belonging to your estate for IHT purposes.
So, if you are concerned that you may die within seven years, and you are giving this person a substantial gift, then a Deed of Variation would be appropriate. This must be done within two years of the death of the person concerned.
You can choose exactly how much you wish to give in a Deed of Variation.
[EDIT]
Just saw the previous post. Yes, this is a good idea as well, to give the carer a life interest in the home if that would be better than selling the home and forcing them to move out.
The only issue there is that you would be faced with a Capital Gains Tax bill when you eventually come to sell the house as you have not lived there yourself.