Monday is a bank holiday, and I have been sent a relevant note from the OCIAM secretary regarding getting into the building on that day. Here is the text of the message:
"Please be sure that you let them know that although their university
card will work on the door that they will also need to use the digital
code and/or ring buzzer 9 for Kate or Peter.
They will also need to get through the white card doors."
The instructions to call '9' should be on the front door, and that will allow someone to unlock the door for you.