This is the problem with joint tenancies.
If you sign one, you are ALL liable for the total rent. As assured shorthold tenanacies are for fixed periods (usually 12 months in the student context), each tenant will have signed an agreement that potentially leaves them liable for the rent for all tenants for all 12 months.
You
might have a landlord that will only go after the defaulting tenant, but you might not. Many landlords will decide, not unreasonably, to pursue those they can most easily and cheaply pursue. And that choice is exclusively the landlords. If one tenant has done a runner, it is likely to be much harder and more expensive (or impossible, such as with a foreign student that has left the country) to pursue that person than to go after the easy targets i.e. those that have remained because they're doing their degree and don't want to jeopardise it.
Another factor in this will be a subjective assessment of ability to pay. If the defaulter is unlikely to be able to pay, even against a court order, and a remaining student(s)
can pay, guess who the landlord is likely to go after? Yup. You got it.
All of this can, ultimately, lead to court action against one person for the default of another. In other words, when entering into a legally binding contract where you can be liable for someone else's default, do
not do so lightly. And bear in mind ....
you picked (or accepted) your housemates, and applied for the property as a group. It's YOUR job to judge the reliability of the individuals you share with …. And to pay the price is you judged wrong. The landlord assesses the group as a whole.
Furthermore, if your parents signed a rent guarantor form, they could be liable for the missing rent of another student, too. My advice would be to make sure that any such guarantor form limits liability to any default of their offspring ONLY .... but note, that doesn't exclude their offspring from being pursued for the default, by court action if necessary. It would only prevent court action being taken against the parent if another tenant defaults.
There are more complications, too. It isn't as simple as just finding a replacement tenant and moving them in. A group of people have a legally binding contract, and it usually precludes sub-letting. It is NOT legal to just move someone else in. The landlord is legally entitled to vet, and approve or reject, any substitution, and any substitution will legally invalidate the existing contract, leaving the sitting tenants owing the remainder of the rent for the FULL TERM of the agreement. While a landlord would be hard-pushed to justify just refusing a new tenant willy-nilly, they CAN do so with reason. So, for that matter, can the other tenants. It might, for instance, change the council tax liability if that new tenant were not a student.
So, any replacement of tenant needs to be done formally and officially, either with the signing of a new tenancy agreement that replaces the existing one, or with a legal assignment that modifies the old one. In either case, the landlord can accept or decline (though only with good reason) to do so. And, in either case, there may be costs associated with it, especially if either the landlord or letting agent have to have a legal document drawn up.
It’s probably unfortunate that student tenancies are often the first real-life, serious legal commitment made by people who were, very recently, children, and that often haven't quite woken up to the fact that the agreement isn’t just a piece of paper and a formality. It often comes as a shock that it is legally binding, and furthermore, commits you to be responsible for someone else’s default. It may not be entirely fair (though it’s arguable) but it IS entirely legal and, if the agreement was drawn up competently, pretty much legally bullet-proof. You can and quite probably will either have to pay up or end up in court if someone defaults.
To my mind, this is a damn good argument for seeking out bed-sit type accommodation, and signing a sole contract, not a joint one. Or, alternatively, find a landlord that will agree to sole agreements for rent and liability over your own room, subject only to joint liability for damage (etc) to common areas. They do exist, and if you know that, they are worth looking for.
Oh, one more thing. The very first thing a landlord is likely to do is use any deposits from ALL students to cover shortfalls from a defaulter. So if someone disappears and leaves rent owing, all tenants can probably say goodbye to any deposit. This is simply because it is the easiest and cheapest way to recover some or all of the default.
And, of course, if rent isn’t paid in full and on time, and no alternative arrangements can be agreed, the landlord can start proceedings for eviction. They take a while and don’t kick in straight away (a couple of months), but if this happens at the start of an academic year … well, I wouldn’t want to get part-way through a year and find myself getting evicted and property hunting. But, if rent isn’t paid …..
There are reasonable protections from eviction (Protection from Eviction Act ), but eight weights of rent arrears is grounds for
mandatory eviction, and that means that if the case is proven, a court has
no choice but to grant possession to the landlord. Going after arrears isn't the landlord's only option.