BUNAC to HSMP?

[Skye Plan]

Hello,

I am currently a US citizen in the UK on a BUNAC visa which expires in mid-December. I am planning to apply for the HSMP but I think I need to leave the country and apply from the US as the BUNAC is only issued for six months. Does anyone know if that's true?

Once I've left the UK and have sent in my HSMP application, am I allowed to travel back into the UK for short trips as a tourist or do I need to stay out of the country until my application is processed? Has anyone heard anything about how long the processing time will be once the HSMP is resumed in December?

Thank you very much!

S