One student wants to leave a joint tenancy and rent not received?

Why would you not have guarantors if they are all students? I appreciate that is not helpful in answering your question but how did you assess that they could afford the rent otherwise?

If I understand this tenancy set up correctly then the present 3 tenants are due to pay the full rent unless they can find a 4th person to join them - though you could consider giving them the next month to find another person and swallow the slight reduction in rent you receive. There are plenty of PhD students and other students whose term does not start until mid October who will be looking for accommodation so this situation could well be resolved very soon.

All tenants are joint and severally liable. If you can't get the vacated tenant to pay their proportion then the other three must make up the shortfall. Or you could give them the option to find a replacement and then draw up a new tenancy agreement and charge a small admin fee.

I think you probably need to take a pragmatic view here. Your 3 students are unlikely to be able to afford the 4th rent and you won't win any friends by trying to make them. You have no guarantors to chase so you are down to 3 tenants for now.
Cut your losses, and replace the tenant with a student found by the other tenants, or tell them the room will be filled by you. Spareroom.co.uk will probably get you a tenant and you will be left with Council Tax if not a student but with a 25 % discount for 1 only. This is better than an empty room.
If you can't fill it - lock it so the existing tenants don't sublet or use for partying/friends.
At the end of the year you have a strong case to keep all the deposits.
I'd release the girl who left once she has stopped paying or her parents won't pay any more.
Next year don't let any one near without a guarantor that you have credit referenced and they stack up. Consider Rent insurance as this has an impact on those who don't pay.
And it's happened to us all, so don't waste any time berating yourself, tighten your processes and move on!

You cannot lock off any room in the property. An assured short hold tenancy guarantees exclusive use of the premises as seen.

Reply to the comment left by "Kelly Joanna" at "23/09/2016 - 11:59":

You're absolutely right Kelly, but we are talking students here. There is also an absolute liability for them to pay, and they aren't. There isn't a legal situation going on here, only an accommodation problem and in my experience, you don't deal with students in the same way as you might other tenants.
I'd still lock the door, and deny them access unless they agree to pay the full rent for the full year - then they are entitled to it.
The situation that YL Newbury is talking about needs "managing", not legal action.

I'm a student Landlord and although in law this is quite straight forward and the comments above correct then it seems difficult in practise. I have been faced with this situation, for various reasons several times. If the tenant who has left fails to pay simply bill all your tenants including the tenants who has left. I charge 1% weekly for overdue rent.

I don't think it a good idea to make payments according to their terms. I let for 52 weeks and expect them to pay late July or August their first payment. I charge quarterly because I self manage. I've never had a problem with this. I don't really understand why you have a lease that requires monthly payments to make an informal agreement of termly which you seem to have made. Such things only lead to confusion.

I think you should let your tenants advertise, strictly speaking, if it's a shared lease you have no right to put in anyone. You could find sources for them in your local area to advise them. www,accommodationforstudents.com is a very good national site for tenants and Landlords.

I think also you should get parental guarantees. They are always easy to get and I only take groups who can supply them from parents within this country.

If it's any comfort when I have been faced with this problem things have worked out ok, but I always made my tenants clear about the situation and would have billed them if the situation had continued, which I advise you to do, especially as it looks as if one of the first payments have not been made and will be soon overdue. I have never in all the 35 years of being a Landlord lost rent and I hope you experience the same.

Reply to the comment left by "Bill O'Dell" at "23/09/2016 - 12:54":

You really are out of order here. Students have tenants rights like every body else and in a shared house the Landlord does not have the right to put in a tenant during the tenancy let alone lock doors.
I've been in this situation and have always resolved it and lost no money.
This is terrible advice and you should be ashamed of yourself.

well you leave yourself wide open for prosecution that's all I can say. The ethic behind your comments, and the discrimination in fact would worry me if you were my landlord!

Reply to the comment left by "Yvonne Francis" at "23/09/2016 - 14:23":

Well that a view too. Like you I am a student landlord and I have never had a void and have always had happy tenants. In my experience students are experiencing their first taste of the real world and you simply cannot treat them like professional tenants. They need a helping hand and some guidance - maybe I didn't make it clear that I don't do anything without their consent, but neither will I roll over and let them go wild. Negotiating a solution that keeps them where they are will be welcomed by them.
I haven't had a void either, and have had happy tenants for 10yrs+.
YL is in a difficult position with no guarantees and could - if too heavy handed - loose all their tenants. Students will respect a landlord who helps them to take control of a situation and provides solutions. Simply demanding rent every quarter won't work with students as they have to often wait for student loans to come through.
And as for charging 169% AER - you should be ashamed of yourself !

Whilst I charge a one off flat fee for overdue rent as I know quite a lot of other landlords do, I can't help thinking that anyone charging a 1% per week charge on overdue rents could be falling foul of consumer credit regulations. In that I mean charging interest on late payments, to all intents and purposes is credit without the valid FCA Consumer Credit Permissions.

I could be wrong but all the same I would be extremely cautious in that regard.