It seems to vary depending on the local authority, I had to supply a year for my mother, however, a friend in another authority was asked for 6 years but he believes (No idea if he's right or not) that the obvious wealth of his mother's large house and its contents wasn't consistent with the fact she was getting by on very little income and the savings had gone although my friend and his sister had been helping her out financially for years. I guess if they see someone who has obviously has been well off they would wonder where it went and had it been deliberately been disposed of or stashed away somewhere.
I had a quick look around and Merton council's on-line form asks you to list any gifts over £500 made in the last 7 years!
If you only had to supply 3 months as leswi did then it would be pretty easy to fiddle.
It'll be interesting to see what the answer is, someone on here is bound to know.
K