Hi Claydon82,
If you're going to get a letter from your employer you might find it useful to ask them for one stating you need a second passport instead. The passport office can issue you with a second passport if you show a need for one, for example for flight crew to obtain travel visas while still travelling for work.
Renewals and visa applications are then much less hassle as you can continue to work using one passport and send the other one off for processing.
I did this myself a few years ago and it has made my work life much easier, especially when the Russians took several weeks over issuing my last visa!
Just a suggestion anyway so feel free to investigate further or disregard as you wish.
All the best,
Chinchilla.