I keep mine on a portable hard drive at the minute- I don't like letting things go :-)

In a previous life I looked at this and there are no set answers. We were looking to protect ourselves from rising insurance costs following numerous (and rising) speculative accident and ill health claims. Some claims have statute time bars but others do not, particularly ill health but we got legal advice. The plan was to be in a position to quickly reject false claims by having the required evidence to do so. Even in the first year we were able to reject a number of speculative accident claims, however all documents had to be archived not just the risk assessments.

I have 40 years is my policy. I just wondered what other people do?

In these days of electronic documents it takes little effort to keep all archives. I have kept everything since I became a self-employed consultant (8 years) and have worked with over 30 customers The RA archives can be useful to demonstrate for example - that the noise risk assessments in a working area were suitable and sufficient 8 years ago - explain to engineers the history, how risk assessments of a particular process have developed over the years, what changes e.g. maintenance, accidents etc were responsible for revisions - evidence for auditors or inspectors that there is a suitable documented risk assessment revision process in place