My last day travelling on the Piccadilly before my office moves to Waterloo and the Metropolitan becomes my normal route in to London. So you know what happened. Signal failure at Ruislip, some trains towards Rayners Lane diverted to Heathrow, no service offered beyond Rayners Lane. Your correspondent de-trained at South Harrow and took a bus, arriving home about half an hour later than normal.
As Harry Hill might have said “What are the odds on that happening?”. Pretty low Harry, believe me.