Draft assured shorthold tenancy agreement

I need suitably qualified person to draft up an assured shorthold tenancy agreement asap.
Flat to be let to one person but permission given for her to let one of the bedrooms to another person on the proviso that if she vacates the flat the other person leaves at the same time, so what we are trying to prevent is the situation where the first person leaves and we are left with a person that we cant get out!
Effectively two agreements I guess one between us and the first person and a second agreement between us/first person and the second person.....unless you can suggest anything more suitable.
This is urgent so please only bid if you can do this \'yesterday\'!
Would prefer if you had current pii. and it is your own agreement and not downloaded from the web!