Please can you advise

Rent Arrears

We have a flat rented to a couple on a 6 month assured shorthold tenancy agreement. They moved in on 4th December and paid us rent and a bond. They were 2 weeks late paying rent the following month (4th Jan) and we had to keep sending reminders. On the 2nd Feb they emailed a list of complaints about the flat to which I responded I would happily sort out but reminded them that their rent must not be delayed again. The 4th of Feb has come and gone and no rent - they have since emailed to say they are having financial difficulty and do not know when they will be able to pay rent. My feeling is that I want them out but am unsure as how to best proceed as this is our first experience of this.
Many thanks