The MG gets a steady diet of 92 or 93 octane E10 that's filtered through a relatively course(compared to a typical FI filter) transparent or translucent plastic filter that sit a few inches from the front carburetor. A while back, I had a bad tank of gas that caused me a lot of issues, and I managed to clog a couple of fuel filters. They were visibly filthy and also were noticeably restricted to the point that it would only flow 1-2 oz/minute(the pump is speced at 15 gal/hour, or about 1qt/min, and an in-tune MGB running at ~70mph needs 5-6 oz/min). Before I got smart and started carrying spare filters, and then got REALLY smart and just replaced the tank and all the fuel lines, I once found myself backflushing a filter on the side of the road just to get me home.
If ethanol did indeed "clean" filters, the above wouldn't have happened. The backflushing worked as a temporary measure for the same reason that backflushing any filter works-it pushed some of the junk clogging the filter out from the opposite direction in which it was actually caught.