Originally Posted by xenole

Depends. Could be anything from £750 for TP run that gives close to 50,000 Avios up to £4k F fares giving 16000 Avios.
Credit card spends, Tesco etc all help towards that.

Realistically (just buying a normal fare and ignoring Amex cards etc), a gold member, or silver at present, would have to do at least 4 x CW returns to JFK to pull in those miles, so anything from £5k upwards.