'There must be suitable accommodation available , which you own or occupy ‘exclusively’ as a couple, though in this context exclusively means only that there is a bedroom for your exclusive use.
You will need to satisfy the Home Office that the property is secure – that is, that you are not likely to become homeless – and that it is not statutorily overcrowded.'
I would imagine that your 'friend' would have to provide you with a form of tenancy agreement.
Your afterthought suggests you are not actually intending to stay in your friends...............
I understand the authorities do not check-up after a visa is granted. However, it may cause problems in the future when you apply for diffrent status and things/issues dont add up.