First UK Passport - When do supporting documents get returned?

I was just granted British citizenship and did not know that I could have applied for my first UK passport at the same time, so now have to do so separately.

I have to send my US Passport along with my naturalisation certificate as they do not accept copies. Does anyone know how long it takes to have these documents returned? I travel frequently for work and can't afford to be without a passport for extended amounts of time.

Thanks in advance!

They'll return the US passport quite quickly.  Within a few weeks at the max.

Great, thanks!