I moved to Sandon Road in 1980. The flooding did happen back then, but was quite a rare event. The first significant one that I saw was due to thunderstorms in 1982, I think. It was fairly quiet after that, for a while, the original culvert was cleared as a result - and the balancing lakes were expanded in 1990. The frequency of the floods has greatly increased in this century. There are a lot of car parks and big tin sheds upstream on Sandon Brook now, which may contribute to the inflow.
I seem to remember there being a dispute about who was 'responsible' for the situation. Blame was circulated around the Borough Council, Severn Trent - even the NHS, via the downstream section running through St George's - there may have been others 'involved', I'm not sure now.