Eviction for vandalism

Possession - Section 8 and Section 21

My tenant has been admitted to a psychiatric hospital under the mental health act. He has severley vandalised the flat - smashing the electric ceramic hob, destroying kitchen units, the bathrrom apparently is 'disgusting', he has thrown out the smke detectors etc. He has been seen making fires with petrol and defacating in the garden.
My questions are:
1) Should I serve a s8 notice? He is not at the flat but in hospital (I think), do I just pop it in the letter box? Is it then served? Can you recommend a firm of solicitors to take this matter to court or is it simple to do myself?

2) Am I allowed access to the flat? I have only received reports from his brother and a builder who met him. I would prefer to instrct an agent to make a report and take photos - do you know anyone that does that or should I use a local letting agent?

Thanks
David