We have also gotten a little worried about the closure of government offices so we have re-booked for Friday. To re-book you have to cancel your initial appointment and you'll get a refund in 5-10 days if you paid for it. I have just re-booked 5 mins ago and there were appointments but only Wednesday, Thursday & Friday but they were pricey at £110 for a standard appointment and £185 for express.
I hope this helps 
Yes thanks! I have also rebooked and paid a bit more . Rather get the visa then not!
