I hear all sorts of conflicting options for gambling income. Premium Bond income would be 'passive', as it's not gambling. Some simply treat it as interest income, which I feel is the better option, (unless there is a very large win - explaining away a profound interest rate would be tricky, but a nice problem to have). The article lists retirement account distributions as general. This i'm sure would be 're-sourced by treaty' though for those in the U.K, with IRA/401(k) income etc.
A big win would indeed be a nice problem to have. Our Premium Bond winnings are reported as interest income. Our US pension income along with dividends from a US taxable fund are all reported as “resourced by treaty”, so I am sure distributions from an IRA or 401k would also be resourced as treaty in order to claim FTCs.