I would second that if money and time off is possible go in person.
You can take all the evidence you have even some you are dubious if it will be useful. Also noticed the ECO or whatever they were called seemed to deal with those with lots of evidence far quicker than those with a small sample from the time we sat around waiting.
You cant lose your paperwork (well unless you are stupid). If that parcel goes missing and the wrong people get their hands on it be prepared for some intresting days ahead.
Its all over in one day no waiting and waiting for days for some news.
The time taken seems to vary greatly, some people seem to have to wait months for the passport back. This means no travel or being able to use it for I.D for opening bank accounts, proving who you are for remittance prehaps or getting a new job.
From the morning we spent at croydon I found the guards and people quite cheerful and friendly as long as you chat to them and be polite. Many other report them as not so friendly.
One guy was so helpful he sat just by the door at the waiting room and we walked past him several times for various reasons. Each time taking the time to smile and chat as we went by.
Most people i noticed just grunted at him as they went past but a quick smile and a how you doing. Meant when later we needed some assitance he went out of his way to help us and i think was happier than the Wife or I when she walked past with her Passport
The same with the security guards when we went back to collect the wifes passport with stamp later on that day. They were questioning everyone who was asking to get entry back in checking id etc as we walked up.
Because we chatted to them on the way in and tried to comply with whatever they asked efficently. They opened the door and greeted us and wished us well as we went in.
Simple Lesson when going to vist a place be polite and friendly to all you met you never know who they are or who they know or how they may help you later on. Manners cost nothing.
One of the most important rule we teach all our Workers who vist customers sites for whatever reason.