Mod1 was most nerve wracking for me, despite knowing I could blow it away.
Have you had any lessons? If not, it is worth just grabbing an hour or two with a local instructor before your test as she/he will take you on the test routes and highlight specific issues, such as hidden 20mph zones etc, and the local expectations (there may be slightly different expectations between different centres across the country).
I'd say the most important thing is to show you are safe on the road, both for yourself and for everyone else, and legal. If you are uncomfortable about overtaking something on an A-road, it probably means it is unsafe to do it, so don't. Don't filter though, it's just not worth it despite what's said above - there are so few regulations and clear advice on filtering that you can be easily caught out - for example, filter towards the front and find there is no safe place for you to pull in leaving a bike length free from the car in front, or end up over the ASL.
As for losing the examiner, I did it about 6 times on my test and he made me pull over every time very quick - basically because without him behind you, you are not insured. These pull overs are also watched like a hawk - mirror, shoulder check, indicate and stop in a safe place.
Examiner made a mistake on my route telling me to take the next right - into a dead-end road! I followed his instructions and then he apologised and said it was the next right - left shoulder check to make sure it's safe to cancel the maneouvre (if not, carry it out and do a u-turn when safe to rejoin the original carriageway), indicators off, return to normal road position, and immediately start again to turn right into the next road. Just take it easy and safe and you will be fine.
There's some brilliant youtube videos where people have just passed their tests and then redo the ride to show the things you might expect. Worth checking them out, plus especially RoadcraftNottingham