It is covered in the ESRC guidelines, on page 33 of the guidelines it states that: "If an award is prematurely terminated for any reason, the student must repay to the RO [i.e. your university] any monies including maintenance grant, fieldwork contribution, etc overpaid [emphaisis added] to them. All debts that arise as a result of over payments, for whatever reason, must be actively pursued by the RO. All reclaimed monies must be returned to the training grant."
The key word here is 'overpaid' - if you have been given the £13,590 maintenance grant all in one go and you quit after 1 month, or 2, then you will have to give back everything but the £1132 or £2264 that you were entitled to for that 1 or 2 months. This is because the funding can be used for other students, so it is vital that the university get as much back as possible, for the benefit of others. If, however, you have only been paid the maintenance grant one month at a time, then you won't technically have been overpaid, and so won't have to give the money back.
As far as the tuition fees go, these are paid directly to the university by the ESRC, bypassing you, the student, so the tuition fees should not be your responsibility as the university should simply refund itself - but check with you research funding office to be absolutely certain. Any Research Support Grant money that you used may need to be paid back also as the purpose of that money is for additional training - which you will not be receiving.