I totally understand that, and this is where the government needs to step up. People shouldn't have to worry about taking the time off. It shouldn't be an issue in a time like this.
In saying that I am almost certain that in 14 days you would be able to get in contact with a GP that would write you a note for the full 2 weeks, most likely over the phone. Wether or not you have the sick leave or your employer comes up another solution is another matter entirely.

On that note, join your union. I'm lucky in that I'm a member of an excellent union that has been working together with my equally excellent employer to ensure that we are fairly compensated should we need time off for isolation.