You ask "
Is there an amount you have to earn ( as in employment ) before you are taxed in retirement?.
Pensioners have a higher personal allowance than younger people. At present the basic personal allowance (i.e. the amount of income that isn't taxed) for someone under 65 is �6035. At age �65 that rises to �9030. However, if a pensioner has an income greater than �21800 their personal allowance starts to go down. (It goes down by �1 for every �2 of income above �21800, but it can't go below �6035):
http://www.hmrc.gov.uk/incometax/personal-allo w.htm
For the whole picture, start here:
http://www.hmrc.gov.uk/pensioners/index.htm
Chris