Stay a well paid GM for a while and use your payslips to start a side business by buying buy to let property. Manage it yourself at the beginning so you can learn the ropes. Once you have a few you can use an agent if you want. Many are useless though.
That is a nice side line business and pension plan builder. Drop any contributions to RA's and other paper assets and pump all into property. You send the tenant to work to pay your asset off. I cannot get much better/more passive.