For UK residents qualifications–you need 600 tier points to advance to silver and on top of that another 1500 tier points for gold. In total 2100 tier points. These points are for renewal as well.
Yes, every time you have reached the next level–your tier points account is reset to “0” tier points. I felt mislead when I first reached silver status and my tier points is reset to zero–stupid me !! forgot to read the small quotes bearing this–I was angry as I have lost a lot of tier points at that time !!
So just in case for the future wait till you change to silver–try as good as the minimum points of 600 or 400 to be recorded respectively and then collect for your gold status—otherwise the tier points are gone !!
It is really indeed a huge difference if you live in UK and need 2100 points for gold, while outside UK you need 1200 points. No wonder that a lot of Brits go for Star Alliance(LH) or Skyteam(AF/KLM).