unkown persons in flat

Maintenance

Received complaint from neighbour downstairs of escape of water damage. Went to investigate to find that there were 9 adult men living in my 1 bed flat let to one male tenant. The condition of bathroom is dangerous with risk of bath falling through to flat below according to neighbours builder called in by him to carry out repairs. First can I go in and start repairs to my flat which will mean no bathroom foe a week and second can I demand unknown 8 adults to vacate without a court order. I suspect they are illegal immigrants so can I report to the police?