I rang the HO and their best advice was to 'withdraw the application' which is hardly an option as my existing visa has now expired. Thanks a million.
I rang my embassy and it turns out they can issue a 'concurrent' passport for 'urgent business travel' where the 'primary passport was unavailable as part of a visa issuing process'. A concurrent passport is a 2nd passport, it does not replace your primary passport.
Re-entering the UK was a surprising a minor affair, the officer stopped me and spent about 15 minutes checking to see if I had an outstanding visa renewal application. Once he confirmed this my passport was stamped with a 'code 1' stamp which has a validity of 2 months. He said the check and stamp had no impact on the visa process or immigration status.
NB Its your own responsibility to check the legality/implications before travelling overseas. Perhaps others with the knowledge could comment on this message.
BTW In my experience ringing the HO for an update is a total waste of time and I beleive forums such as this do a much better job of keeping people informed of the timelines. Perhaps if we leave the HO alone they will then allocate the excess call centre staff to the case working area
![Wink ;-)](./images/smilies/icon_wink.gif)