Having submitted my application and booked the appointment I've realised I have made a mistake I was refused a visitor visa before through missing documents. But I clicked 'no' to this option on the form. Will I be okay to put a cover letter in explaining I made this mistake and explaining why I was refused? Otherwise I have to wait another 3 weeks for an appointment if I cancel and submit again.
Better cancel the application and take a new appointment and correct the mistakes, otherwise you might be ban for misrepresentation. Don't take a chance on covering letter.
Yes, decided on that course of action. I also realised I made a mistake with the travel history which may actually HELP my application! Serves me right for rushing it but I was rushing because appointments were going so fast. Now I got an e-mail today saying they realise there has been a problem and they are going to open up new slots For goodness sakes, VFS / Home office - get your act together!