help let flat to friends

chappers

If you want this to be a temporary thing then it is imperative you set up an agreement.
Be VERY VERY VERY careful of this situation, if things turn sour, and they can, I speak from experience. You could end up losing a friend over this.
Also as Clutton says you seem to be totally un-aware of your legal requirements.
I was in a situation where I rented the self contained basement in my old rental house, to a friend and his wife when they were skint. This was meant to be short term, until they found somewhere else, as they had just got married and didn't have much money I agreed to lend it to them at much reduced cost with no bills.
A year later it got so bad with them repeatedly saying they would be leaving next week , next week, next week.They were staying out late and avoiding me, they changed the locks to there main door and fitted bolts to the door connecting the basement to the main part of the house. eventually things got so bad that I had to take legal action to get them removed (without a proper contract this was a nightmare). Eventually I got a court order for them to leave this was after they had been staying with me for nearly 2 years. Unfortunately this date was whilst I was away in America for 3 weeks.
On my return they had moved out but had taken all the furniture, crockery, cutlery and had smashed bottles of sauce and basically anything that made amess all over the walls and carpets.
all this from someone I had known very well for 6 or 7 years.
Now I know this could of happened with unknown tennants but I would have not let the situation go for this long if they hadn't been friends.
I would proceede with caution here and the least you need is a proper contract between you. i would be very wary of using a formula contract as each rental situation can be different